Ensure the _msdcs zone is healthy and populated with records on your primary DC.
You might simply be running DCDIAG without administrative privileges. Dsreplicagetinfo(Pending_Ops Null) Failed Error 0X2105
Run: netdom resetpwd /server:Source_DC_Name /userd:Domain\Admin /passwordd:* . When to Rebuild Ensure the _msdcs zone is healthy and populated
If the DC has been offline longer than the or if the metadata is severely corrupted, the most reliable path may be to perform a metadata cleanup using ntdsutil , demote the server (forcibly if necessary), and re-promote it. demote the server (forcibly if necessary)
A common culprit for "access denied" is a misconfigured computer account. Run DCDIAG /TEST:MachineAccount on the affected DC.