The RPC (Remote Procedure Call) server error appears when some of the RPC-related services are not functioning properly. This is not caused by network scanning per se. It is usually related to disabled file or printer sharing, network connection interruptions, RPC-requested traffic being blocked by the firewall, or corrupted registry files.
Here a quick overview of what can be wrong and how it can be fixed:
Fixing "The RPC Server is Unavailable" error in Windows.
If that doesn't help, Microsoft provides a detailed troubleshooting guide:
Windows Server Troubleshooting: "The RPC Server is Unavailable".