Is RPC Server unavailable secure or not on workstation ?

Hello,
I recently installed Lansweeper on my server. When I check the reports, I have 16 pcs showing “RPC Server unavailable”.
It does not seem a big issue (I can communicate with the stations) but I was wondering if I had to activate the service on all missing computers.
Is it secure and/or useful ?
Server is SBS 2008R2.
Thanks for the answers.