[TYPO3-calendar] Backend Login failure after upgrade to 1.40

[Jörg Schreiner]

Hi,
I upgraded the cal extension to 1.40 and was immediately thrown out of the 
Typo3 backend.
Every backed login now fails with an error message that leads to the 
conclusion that Typo3 is forgetting the login name for any reason.
I'm not quite sure, whether this is a direct problem of cal but maybe a 
misconfiguration of  anything else (e.g. .htaccess) but the new version of 
cal seems to make this problem happen.
Any hints/suggestions appreciated.

Thanks Joerg