[Security] Forum keeps logging users under different accounts

[MR.sugar]

Hello,

I'm experiencing very strange problem with my forums. Suddenly, forum started to log users under different accounts.

For example, when I log in as MR.Sugar, after while, it says I'm different user.

Never heard of this problem, anyone have idea what could cause this? I had not installed plugins or changed settings.

Here is the forum: http://tripminestudios.com/lazorcat/

I also tried to upgrade to the latest version, but no help.

[frostschutz]

This user has been denied support.

server side caching gone wrong?

[MR.sugar]

That's possible. Any ideas what steps I should take to get things back to normal?