Can you do a "save config to flash" to the same controllers successfully? If you then do a refresh config from controllers" with delete is that successful?
If the save is successful and the refresh is not I'd say and issue with mtu over the vpn maybe. Check to to see how many varbinds you are sending under Administration > Settings > SNMP Settings. If it is greater than 50 change to 50 and save then try the test again.