Verify that the NTDS VSS writer is stable

From an elevated command prompt run the following command:

vssadmin list writers
The results will appear as:
Writer name: 'NTDS'
Writer Id: {b2014c9e-8711-4c5c-a5a9-3cf384484757}
Writer Instance Id: {ee24b741-eaf7-4663-8f95-b92ae8c5e164}
State: [1] Stable
Last error: No error

If the NTDS writer is not listed as "State: [1]Stable", reboot the DC (Domain Controller).