[TYPO3-english] TYPO3 4.4 Logging me out!

[I.Sprock | Idar Creative]

Hi List,

I have an unusual problem.

It's not possible for us to work simultaneously in the same backoffice of 
our TYPO3 version 4.4.
When my colleague goes to the login page (not even logged in), the TYPO3 
logs me out! (without even an warning) and visaversa.

In the DB we see one BE user session is created instead of two.
All the localconf settings are not changed. (standard)

What may cause this problem?
Is it something to do with IP, or else?
Can anyone give me some pointers?

Kind regards,

Idar


ps: The project has a bit of a hurry, so any suggestions are welcome.