Linux (Ubuntu): Can't open the file shared

I’m on ubuntu 13.10 (on an old 2007 pc) and if I launch Garry’s Mod after a while I have this error:

http://i.imgur.com/ZlCHqWs.png[/t]

(the italian part could be translated with “Can’t open the file shared: File or directory doesn’t exist.”)

but I can find the directory AND the file:
[t]http://i.imgur.com/JsMYaxQ.png[/t]

If I launch the game again Steam downloads something:
[t]http://i.imgur.com/mjMBboh.png

P.S. I’ve also tryed to verify integrity of game cache, but it didn’t help.

Thanks in advance for your help

[editline]24th December 2013[/editline]

I have found a solution:

sorry, I should have searched better before making this thread.