Hi,
This error can be two things
1- Communication including CM and vCenter .
You can add these variables in both server in the file omnirc file:
OB2SHMIPC = 0
OB2IPCKEEPALIVE = 1
OB2INETTIMEOUT = 10
OB2IPCKEEPALIVETIME = 900
OB2IPCKEEPALIVEINTERVAL = 60
2 - Can be having snapchot the Snap manager, verifies that each virtual machine , and if you find any delete it and sends the backup again.
Regards