[Typo3] FEUser->BELogin, Problem with 3.8

[Soenke Schippmann]

After updating a testsite to version 3.8, the "feuser->belogin" 
extension does no longer work. Frontend login does work, but when I 
click on the CMS login button, I get typo3's standard authentication 
error: "Your login attempt did not succeed. Make sure to spell your 
username and password correctly, including upper/lowercase characters."

Any ideas?

Thanks,

Sönke