session setup failed: NT_STATUS_NO_LOGON_SERVERS

Hello,

I have a ReadyNAS Ultra 4, fw: RAIDiator 4.2.24.

I have set up 7 backup jobs 2 years ago, all of them are manually started, no schedule, all worked fine every time I started them.
The source of the backups is my laptop with Win 7 Pro. Nothing was changed on my laptop, nor on the ReadyNAS. 3 days ago I ran these jobs sucessfully. Today I go this error for all jobs:

----------------------------------------------------------------------------------
FULL Backup started. Sat Oct 26 00:36:10 CEST 2013

Job: 003
Protocol: cifs-ab
Source: //192.168.1.4/c$/Nollex/
Destination: [backup]//Nollex_backups/

session setup failed: NT_STATUS_NO_LOGON_SERVERS
Files copied: 0

Backup finished. Sat Oct 26 00:36:15 CEST 2013
----------------------------------------------------------------------------------


What can be the problem?


Thanks in advance!
Gyozo