WHile creating a new account, two strange things occured:
After generating a mail with link to complete the registration, a neat red colored text shines on top of the page:

SYSTEM WARNING: session_destroy() [function.session-destroy]: Trying to destroy uninitialized session

Okay, why not. Anyway, while changing the password and pushing the submit button ONCE(re-tested twice!), the following happened:

APPLICATION ERROR 2800

Invalid form security token. Did you submit the form twice by accident?

Please use the "Back" button in your web browser to return to the previous page. There you can correct whatever problems were identified in this error or select another action. You can also click an option from the menu bar to go directly to a new section.

From here i can work normally... until i log out. After logout, i cannot login again.