Start by verifying all servers have the latest BIOS and ESM firmware installed. You stated that the server agent is 4.51, but different models of servers do not support the same version of the agent. If you install Server Administrator 1.4 on each managed server, the correct agent version should install by default. Also, verify that the Dell Server agent and Dell server agent monitoring service are running in Services on the managed servers.
You may also want to verify that ports 161 and 162 are not blocked by the router.
Another good source of information on Open Manage software can be found in the May addition of Dell Power Solutions magazine, http://www.dell.com/us/en/esg/topics/power_power.htm.
Dell Forum Administrator,