Steps to troubleshoot "RPC Server Unavailable Error" when adding Windows Server through WMI mode in OpManager.
1) Try to add the server using domain-name\username and with username alone.
2) Check whether you are able to ping the remote windows machine from the OpManager Server. Try ping with both hostname and ipaddress.
3) Check for any firewall between OpManager Server and the remote windows machine. If there is a firewall , then you have to open up the ports in firewall for monitoring. The ports are 135 (RPC) and 445 (WMI). Then try adding it in OpManager.
Even after opening up the ports, you might get the same error. WMI in the remote machine may use some random port to reply back to the WMI calls (that you make to the remote server from Opmanager Machine). However, you can restrict it to use some range of ports only. So, it is necessary that those ports should also be opened.
More information and procedure about how to restrict the allocation of random ports to some specific range of ports is available in the following link.
the above configuration should be done in the remote machine that you want to monitor.
4) Check whether the RPC and WMI Services are running in the remote machine. In the remote machine go to Start --> Run --> services.msc check whether the Service Remote Procedure Call and Windows Management Instrumentation is running. If it is not running, start those Services and try adding it in OpManager.
5) Use wbemtest to find the error message when connecting to the remote system.
Click on Start --> Run --> wbemtest
It opens up Windows Management Instrument Tester. Click Connect button. In the first text box (root\default) , give the <\\hostname\root\cimv2>
Give username and password. Now click the Connect button. If it gives error, try giving the ipaddress in the place of hostname. <\\ipaddress\root\cimv2>
If it works only through IP address, then only through IP address you would be able to access the machine. This may be due to some wrong entires in the hosts file in
<C:\Windows\system32\drivers\etc\hosts> file. Remove the wrong entries in the file and try with the hostname.