[TYPO3] after update to 4.1 fe users login doesn't work (newloginbox 3.01)

[joachim]

hi there,

i updated to typo3 4.1 and now my fe users login doesn't seem to work 
any more. i then updated the version of newloginbox (was 2.6 or so) to 
3.01 but it still doesn't work.

i believe that there is no problem with finding the user in the 
sysfolder because the 'i forgot my password' function works. it sends me 
the correct username / password. but still i cannot login. when i try 
(using this username / password...) i get the message configured for 
"Login Error" in my newloginbox content element.

i still have an old version of the installation where the login works 
fine. but i don't know how to go on stroubleshooting from here. could 
anyone please help ...

thanks, joachim