[Oreo]

Are you positive this link that you went to did not d/l something into that account? Also, with 6.0 the5.x versions are going bye bye as far as upkeep and support. I know what you mean about the offlines, I had to back a bunch of them up when I switched to 6.0. But this way Yahoo! protects against any problems that might occur. Also, what might be the problem is the number of messages you have stored. Do you have your messages archieved? I'm trying to remember back to that version what I had to do when this happened to me....I believe the culprit was a nasty offline...I think I fixed it by accessing messenger via my cellphone and deleting the offending message and then things worked well again.
What you may have is a bad message stored in your box causing it to crash. (Hence the reason Yahoo! stopped storing them). If you have access to a mobile phone that can access Yahoo! messenger for free or if you have a friend that you trust who would do it for you...that might be your best bet. Good Luck and post again if something changes or none of these suggestions work.