I don't know if it's just me or what but I just went to modify the first post in my 100 SF essentially thread but got sent to a "you can just modify any page" page. The board had me listed as a GUEST. When I clicked to log in the log in page had me listed as KESTER PELAGIUS. When I went back to the forum and clicked on the thread to modify the post I appeared to be logged in but when I hit enter I got sent back to the main forum page as GUEST and, apparently, my edit didn't take.
Took two tries to log back in. When I went to modify the post it appeared as I modified, even though it didn't when I read it, by which time I had reverted to GUEST again.
I've cleared my cache several times. And, so far, this problem doesn't seem to have recurred anywhere else.
Just me?
Most likely a problem with the session authentication. If you are behind a proxy, that could cause this behavior. Ditto with some antivirus/firewall programs.
I have helped a few people troubleshoot problems like you describe since switching the forum to SMF. Deleting the forum cookie and clearing the cache always seems to fix it.
You might also want to check that the time displayed is correct. The date and time appear in top user information box, right under "Show new replies to your posts." If the time offset is not correct, it can cause problems.
However, more than likely the issue was with the forum cookie on your computer. If it is working now, you should be good to go.