Go to Manage --> Appliance in the GUI console. Under the Properties pane, pick "Settings." Look for the Current Default Agent.
Is that a valid hostname or IP? Is that Agent on-line? Does that Agent have the right network configuration? The LEM sends all those Explore commands to the Command Agent, and has the Agent execute them. This way, the LEM and the web console aren't trying to execute strange network queries, but if the command Agent is off-line/unreachable/isn't allowed to run nslookup or traceroute/doesn't have the right network configuration, then they won't work.