Steam - all modules suddenly 'not authorized'

Hi,

just wanted to start the game. And after this "getting steam authorization data" - which happens since a few days - it says "error getting validation data - 504" and then the next message tells me that all my bought modules are disabled..

Http 504 is a Gateway timeout.

What happened?!?

Edit: just realized that I also cannot enter the Community Hub in the Steam Client.

Regards

Jens