You may encounter the following error when connecting to a server in Spotlight:
'Error 0x800706BA: The RPC server is unavailable. Exception from HRESULT: 0x800706BA'
The Diagnostic Server is not able to establish a connection with the target computer.
Please check the following:
1. The address of the server is entered correctly via the Spotlight Connection Manager.
2. The Remote Procedure Call (RPC) service is running on the target computer.
3. TCP Port 135 is open both to internal traffic on the Diagnostic Server and the target computer.
WMI opens an undetermined port in addition to port 135. This can be troublesome in a firewalled environment. Specifying a port range for WMI is recommended for this type of environment. See "WMI connectivity" in the Spotlight on SQL Server Deployment Guide for instructions on how to specify a port range. The use of port scanning
4. If for example, the Spotlight connection is made over VPN, and the link becomes unresponsive, after reconnecting to the VPN and trying to reconnect to the Spotlight connection again via WMI, the error 'The RPC server is unavailable' may also appear.
This is because the machine that was issuing the WMI call to the remote host is using a stale connection that no longer works, because it was established before the VPN reconnected. The Diagnostic Server code issues a WMI disconnect and connect when it gets the RPC server error, but WMI seems to maintain a connection behind the scenes, despite what the code tries to do. When trying to connect with WBEMTest, is also fails, which determines this error is not a Diagnostic Server code problem. It appears that this service retains WMI connections to other hosts that don't work after the network connection between the machines is disconnected and reconnected.
To solve this, rebooting the Diagnostic Server host machine can fix it. If a reboot is not possible or desired, just restarting the Windows Management Service on the Diagnostic Server host fixes the problem.