We're sorry but a serious error has occurred in the system.
If this happens to you, I have a possible quick solution (if you just want to get to the page in question):
Use your browser's menu option to have it create a "new private window" (FireFox), or "new incognito Window" (Chrome), or "new session" (IE), or the like.
This will open a new window for your browser, and it will NOT send any cookies to the page in question. And you should find that suddenly the forums "work", which tells you that the problem was about the server's unhappiness with something about the cookies in your browser.
If that's enough, great. If you want to know a bit more, read on.
You may also find that just opening a different browser than you are using may also work, for a similar reason. Or you may also find that if you close your browser, entirely (all open tabs), and then re-open it, that will work also. Or finally you could "delete your cookies", but that may be more trouble than it's worth for some readers.
I just wanted to give the quick solution above that may at least get you into the page you were trying to access but could not. I didn't see anyone else proposing that in the few discussions on the web I saw on this problem, so I wanted to share it.
So, what does problem and solution this tell us?
Why does this work? Well it seems somehow the forums server didn't like something about the cookies that were being sent from your other browser window (which was failing). It may indeed be only temporary.
What we can know from this "solution" is that this is not a server error (at Adobe) that meant "the forums are down". I saw some threads where people were interpreting this problem as that. I suspected that would be highly unlikely. Still, after a few minutes when it still wouldn't work, that's when I suspected it was a cookie issue, and the solution above worked.
So, what is the problem?
Someone may wonder, "well what is really going on". I can't say for sure, since I don't know what the server is unhappy about the cookies.
What I can say, for any interested, is that I had the same forum page open yesterday, in the same browser--where yesterday it was working, and today it failed.
There's nothing I had done on my end to explain it suddenly "failing". I had not restarted the browser, nor had I gone to any other Adobe forums pages (in any windows of the browser) since it worked yesterday.
And I've often left my browser sitting on a forum page, even overnight or for days, before refreshing it and had no problem. This was the first time I got the error above, but I see on the web that others have gotten it as well.
Some more details
FWIW, the url of the page which was *failing* looked like this:
And I had indeed been sitting on that URL listed there as the "referer". So it was something about the authentication process (since it redirected to this adobe_login page), when I re-requested the other page.
I suspect this is some sort of temporary problem, which probably could clear itself in time.
But again, some people complained that it was blocking them for a week. And that led to them raising the problem in forums, where others talked about "clearing cache", "clearing cookies", and so on. Those could work, of course.
But for some people who don't know better, they may clear "all cookies" or the cache for "all sites", which is overkill. Some know how to delete only the cookies or cache for a given site, but it's different in different browsers, and I don't want to elaborate that here.
One wrinkle: if you want to signin also
I will add that while the above workaround will at least let you VIEW forums pages, if you do want to "signin" such as to add comments, you may find that even in the new private/incognito window, you get the same error when you try to "signin". And taking that URL to another "new private/incognito window" will NOT help, in my experience.
At this point, you may have no choice but to delete cookies, or try closing your browser entirely (all windows), or try to login from some other browser. If I learn more, I will share it here. Still, the tip at the top will help some folks at least be able to READ the forums when blocked this way.
Again, I just wanted to give a quick solution, even if it may be only temporary.
If you find that after closing and re-opening the browser that things till don't work, then look into deleting your cookies. I really don't want to elaborate on that here, so google it to find the details for your browser. :-)
Anyway, hope the tip at the top may help someone else who's suffering this to get in, even if only temporarily.