[TYPO3-english] Problems after upgrading to 4.2.8

[Marco Behnke]

Hi,

I recently upgraded our Typo3 4.1.5 to 4.2.8.
Everything went fine so far with one big exception:

Everytime I open a user record, the text input fields are left empty and 
saving alsways asks to login.

E.g.: If I open user XYZ I can see all dropdowns and lists filled but 
username is empty.
When I try saving I'll get a prompt that tells me that my sessions has 
probably timeout and asks to log in again.
If I say YES a new window opens which tells me that I'm logged in.
If I press cancel, the record is saved losing no information.

If I create a new user, it is saved with login and password.

The same problem occurs when editing content.

Anyone who can help me with that?

greetings
Marco