Here's another entry in my
CF911 series. If you try to open the CF8 server monitor and get the error "ColdFusion Server is unavailable", the problem may be in your web server configuration. In this entry, I help you confirm if you're getting the problem I refer to here, and of course I show the solution (3 actually), with a caveat.
Here's a screenshot of what you may see: 
Note that this is not an error related to logging in. You do need to fill in a username to log into the Server Monitor, even if CF is set to only ask for a password when logging into the Admin. Just use "admin". This and other facets about the CF8 Server Monitor are covered in a 4-part series of articles I did in the Adobe Dev Center, starting here.
Confirming this is the cause of your Monitor challenge
From my observation, this error is related to a problem with the Flex client being able to talk to the server using a URL it needs to use, and the problem is web server related.
You can confirm if what I'm about to describe is your issue by trying to access the URL that the server monitor tries to use to access the Flex Gateway for CF, such as:
http://localhost/flex2gateway/
Actually, you should use whatever domain name/port you're using to access your CF Admin, which is then used when you ask it to open the CF8 monitor, which may be a URL like this:
http://yourserver/CFIDE/administrator/monitor/launch-monitor.cfm
Anyway, if that test attempt to open the /flex2gateway/ url comes back with a "file not found" (or 404) error, as opposed to a blank page, then you likely have the problem I'm describing, whereby your web server is mistakenly looking to verify that a file exists for the path you're specifying. You have 2 solutions.
First, let me note that this flex2gateway URL is not a file, nor a directory. It's a value intercepted by a servlet filter defined within CF. You need to tell your web server not to check for any existing file (it's trying to use one of the "default documents" that are used when only a path to the web server is provided.) Before launching into how to fix your web server, you may want to consider one other possibly simpler alternative.
Changing to use the Internal Web Server
Some will note that I've used no port above in the URL. That's why I point out for you to try whatever URL is used to access your Admin. In the case above (and the people who have reported this problem so far that I've seen, they've been trying to access the CF admin using their external web server, IIS.
If instead you were to use the CF internal web server to access the CF Admin, you'd have a port in the URL, like this:
http://yourserver:8500/CFIDE/administrator/monitor/launch-monitor.cfm
(or it could be 8300, or 8301: whatever is the port for accessing the built-in web server for CF, if you chose to implement that when CF was installed, and you are accessing the Admin that way.)
Well, I'd propose that if you DO use the internal web server, you probably won't get this error at all. The problem seems related to using IIS to access the Admin (and the CF 8 Server Monitor).
That said, I'll suggest that one quick solution folks can try is to see if indeed they can access their CF Admin (and monitor) using the internal web server. (If you can't or won't use it, I have the solution for getting it to work with IIS, in a moment.)
You just need to know what port to use to access the internal web server, if it's enabled.
First, you may find that if (on Windows) you use Start>Programs>Adobe>ColdFusion 8>Administrator that it will open using the built-in web server. If it does, see if using that gets you around this whole problem.
If that opens it with external web server (doesn't use a port like those above), or if you aren't on Windows and have no Start menu, you can also get the web server port (and indeed enabled it, if disabled) by way of the jrun.xml file. Rather than detail it here, I'll point you to a couple of resources:
Configuring the Macromedia ColdFusion MX built-in web server is an old technote, but the info still applies. Where it talks about disabling the internal web server, you'd want to reverse that, of course. There can be more subtleties and challenges to running the CF admin on the internal web server, if you don't configure it that way at the start, such as where are the /CFIDE files? Are they in the [cf]/wwwroot? or in your web server doc root, like inetpub/wwwroot? The built-in web server will look for them in the [cf]/wwwroot, so you may need to copy the CFIDE into this directory, or add a mapping to the built-in web server to point to the path as being located externally.
Making the change in IIS
Or you could just fix IIS to let you access the server monitor via IIS. The problem may be due to a setting in IIS (verify that files exist) that you may have caused to be set. (I don't know if it's set by default when CF is configured to integrate with a site, but I wouldn't think it was, so maybe this affects those who add new sites or configure things manually.)
And since this problem may affect other Flash/Flex apps trying to talk to CF, it may be worth doing for all such users. But this does come with a caveat to be aware of, if you might be using NTLM security to control access to files requested via IIS. More in a moment.
I offer the solution for IIS 6 and 7. I don't know if the same problem can affect Apache. If so, and anyone can offer the solution for there, please do comment.
Making the change in IIS 6
For IIS 6, launch the IIS Manager and select the web site which has the CF Admin you're trying to use. (It may be that you've also configured IIS so that ALL web sites are configured for CF, in which case this setting would be not at the site-level but at the root server-level, so you'd select the server name instead in the left IIS pane.)
From there, right-click and choose properties, and then select the "home directory" tab, then in the "application settings" area click the "configuration" button, and in the "wildcard mappings" section you should see something like "C:\ColdFusion8\runtime\lib\wsconfig\1\jrun_iis6_wildcard.dll" (which will be different, of course, for the JRun4-based Multiserver deployment).
This value is implemented here during the install of CF if you tell it to integrate with IIS, or by your running the CF Web Server Configuration tool after the fact.
Select it, and choose Edit, and if the "Verify that file exists" option is checked, un-check it. This setting can be confusing: you may think it means "verify that the named executable exists", but it doesn't. It refers to whether files requested and passed through this handler should be checked to confirm if THEY exist. Here's a depiction of the setting and how to get there.
Now try the URL above, and it should no longer give a 404. Then try again to login into the Admin. (Actually, you may find that you can just click the "cancel" button and it will login, even if the values for username and password are blank. I find this helpful when the CF server is temporarily unresponsive too, and the Monitor login screen pops up.) Hopefully the server monitor now works for you.
Note that this was NOT about changing the handler mapping for .cfm files, which also offers an option to control the "verify that file exists".
A caveat about access via IIS to NTLM secured files, and another alternative
Thanks to Mike Gillespie for the following notice and clarification. If you use NTLM security (windows integrated authentication in IIS) to secure files accessed via IIS, then you DO NOT WANT TO make the above change for your IIS site. I share below what he offered to me.
But I'd point out again that even with that issue, you could still use the built-in web server is a solution. Or, sticking with IIS, you could also create a new IIS site just for accessing the CF admin and monitor, and make the change above for that site only.
Anyway, if you do use NTLM security to control access to sites requested via IIS, consider the following:
The check that file exists option is required if you want to use NTLM perms to secure .cfm files. http://www.adobe.com/go/tn_18516 (Steps 1-4)
If you have a secure folder on your webserver put a .htm file and a .cfm file in it. Do not give your ID access to that folder. In IIS turn on clear text and NTLM auth.
With the "check that File Exists" option unchecked, try this test.
Try to access the .htm file in the browser - access denied
Try to access the .cfm file in the folder, - access GRANTED - so much for NTLM perms
Now check the box and try again (you will need to recycle cf and IIS)
Try to access the .htm file in the browser - access denied
Try to access the .cfm file in the folder, - access denied as it should be - but flash forms and server monitor are dead.
So "fixing" the Server Monitor problem on an authenticated server just broke the security of the server for the sake of monitoring... [frown>]
In a nutshell.
If you implement this so that CF pages can be authenticated against Windows Security http://www.adobe.com/go/tn_18516, then Flash forms break (and the server monitor too). So to get flash forms (and the server monitor) working, you have to implement this, which fixes flash forms (though every user gets their own personal file on disk on the server that has to be cleaned up) but it does not fix the server monitor.
It is the "check that file exists" selection that breaks the Server Monitor (and flash forms).
On a cf webserver that grants anonymous access there is no reason to check the "check that file exists" box. However, on a server that does authenticate users for NTLM file access, that box should be checked.
This section above was added after the entry was first posted.
The change for IIS 7. None needed?
For IIS 7, it's a little different. I actually run IIS 7 (Vista) and am not sure how/where the wildcard mapping equivalent got created (I may have fudged it manually), but it's now listed as a "Handler Mapping" (in the properties for a web site). In my case, it's labeled "AboMapperCustom-32635", but just look at those listed as handling "*" meaning all requests. It's listed with a value of IsapiModule in the Handler column. (If you're looking at a specific site, and the "Entry type" column says "Inherited", then there is another mapping at the server level, so select your server name in the left IIS panel, and repeat.)
Even so, I see no option to control "verify that file exists", so maybe this problem can't happen in IIS 7. I will say, FWIW, that there is indeed a an equivalent to that "verify that file exists" option, at least for specific extension handler mappings. Look a the one for .cfm, for instance. Double-click it to see its properties, and note a new button called "request restrictions". It has an option, "Invoke handler only if request is mapped to", and an option of "file". Again, though, this does not affect requests to non-cfm requests like that for the /flex2gateway/ URL.
About other Flex/Flash apps
As I said, it may be that the info above will help other Flex apps having trouble talking to CF (the CF8 monitor is a Flex app), but I'll note that this problem doesn't affect all Flex apps: only those that connect to CF via IIS.
For instance, on this same server where this problem occurred, there was never any problem using FusionReactor (which is also a Flex app). It was working fine the whole time. But then its default behavior is also to use its own Built-in web server, so requests weren't going through IIS. If I did try to use IIS to access FusionReactor, then it too failed (with a file not found), and the fix above solved that.
