Studio 2015 unable to update and crashes

Hello! 

I have a problem since this morning: when I start Studio 2015, it keeps trying to update but the update client cannot connect to the server, nothing happens, and Studio freezes.

I deactivated the automatic update but when I open a file to work on in Groupshare, Studio crashes again (I tried to open another file, not in Groupshare, and it worked).

I tried to perform an update manually and it still crashes...

Any idea?

Thanks a lot in advance for your help!