Need to login after sorting accounts

[regenerate]

Hi all,

My sugar installation show a little bug, I'm wondering if it's a general bug or something specific to my system (see my signature for system specs). I executed an upgrade from 5.0 to 5.1 three days ago and worked in sugar a lot since (all through the sugar panel itself, I didn't touch the code or something) so I have no idea what caused this problem.

The problem:
When in the accounts tab and clicking on any of the seven tables labels (Account Name, City, Phone, Website and some custom labels), I get the 'Welcome to Sugar' login screen that tells me: "Error: You must specify a valid username and password.". Besides that, I don't actually get logged out of the system, I can still click on 'My account' for example and continue working with sugar without actually login in again. But the tables still aren't sorted different.

I also have this problem with 'contacts', but not with sorting any other tables (like task, campaigns, . I only have around 40 items in both contacts and accounts.

Any suggestions on how to solve this problem (or finding the cause)?

Thanks!

EDIT: No idea why, but actually login out of sugar and back in again worked, I can now sort again...

[kinshibuya]

What does your sugarcrm.log and apache/logs/error_log says?