If you receive:
Operation could not be completed. The RPC server is unavailable.
when attempting to add a printer, it could be that Spoolss.dll and/or Spoolss.exe are missing or damaged.
Re-apply your latest service pack and insure that the RPC service is set to start automatically:
1. Control Panel / Services / Remote Procedure Call (RPC) Service / Startup / Automatic.
2. Restart your computer.
NOTE: Make sure that the Spooler service is set to a Automatic and is starting.