[TYPO3] BE session gets killed

[Sacha Vorbeck]

Hi,

I`m currently testing a new internet-provider and router and can use the
Web as usual. But when I try to log in to TYPO3-Backends, I`ll be thrown
out either immediately or after a very short time and the message

"Login-error or session timed-out
No user logged in! ...
click here to re-login."

appears.

As it seems both my external and internal IP-addresses are not changed.
Has anybody already experienced something like that or can someone give
me a hint on what might be causing this

I guess there can be a lot of reasons but I just don`t get it atm. Other
session based stuff like online-banking works.

-- 
thank you - all the best,
Sacha