Actually, when it was coming up, it was different places. One time in a thread, one time when you clicked on new posts, one time when you clicked on today's posts, etc.
Ever since I did the file verification and replaced the 4 files that were edited yesterday with the 4 files I had saved from a few months ago, nobody seems to be having the problem anymore.
Of the files that were changed, one was member.php - so a guest may not get the problem to duplicate right? Only members could be having this problem??? Another file that was changed was showthread.php. I reverted that one back to the backed up one, too.
I will post or message you if it pops up again. I have my members making a screen shot of the error from their computer and sending it to me so I can see what happens.
Could this be something that was affected by http://community.mybb.com/thread-105780.html