[TYPO3-english] Login Problems with Typo3 4.3.1 (and also 4.3.2) after PHP upgrade

[Andreas Cord-Landwehr]

Hello,

I've BE login problems after PHP upgrade from 5.2.11 to 5.2.12. Login is not 
possible for every BE user (even for new created ones).

What I tried yet:
* clearing of all caches
* enabled all debug modes, but no errors were presented.
* checked apache-logs, but no errors found
* cleared browser cookies, tried another browser, but didn't help

I'm using MYSQL 5.0.51a.

Looking forward for any suggestions what to try.

Greetings, 
   Andreas