We experience login problems after the wintertime became active. Users do see the site for 1 second and then the profile.php gives an error. After removing your cookie the login problems are solved. Any idea what can cause this? I run a vbulletin integration.
It seems that the problem was caused by an error in one of the vbulletin tables. I repaired the tables and now everything seems to be fine again. Thanks a lot for your reply.