AutoEnrollment errors - RPC server is unavailable

I am getting some problem on a DC where I get the 2 error messages written below:

Automatic certificate enrollment for local system failed to enroll for one Domain Controller Authentication certificate (0x800706ba). The RPC server is unavailable.

Automatic certificate enrollment for local system failed to enroll for one Directory Email Replication certificate (0x800706ba). The RPC server is unavailable.

Can anyone tell me how to solve this problem?

The error that you are getting usually means that the CA is not available or the CA service has stopped. Can you check CA service and connectivity, FW, etc. Hope that this helps you out.