snmp fails after restore
 

I have a problem that I have seen a number of times with snmp on linux.
If you restore a linux server from backup to a different server, snmp becomes almost unusable.
Prior to the restore SNMP works fine, we use SNMP to graph system performance as well as a number of other things.
After a restore has happened, snmp becomes unusable. Sometimes "snmp gets" work but most of the time they don't.
We are using redhat on Dell servers. This week I had to restore 2 servers to differnent hardware and now both of them are unresponsive to SNMP gets.
Has anyone seen this behaviour before?

Thanks
Nick