Backup stopped working with no log on linux Centos

I’m running server 2.2.11 under Windows Server 2012 R2 and client on Centos 5.8.
Everything went good until one week ago.
Now if I try to start a backup from the server the job is queued and then it disappears with no log message on the server nor on the client, both in debug mode.
From the panel I can see the client is reachable and I’ve restarted the service with no luck.
Any hint?