When This Error Hits
You're trying to join a Windows 10 or Server machine to a domain, or maybe a client's old domain-joined laptop suddenly can't authenticate to the file server. The exact error: STATUS_MUTUAL_AUTHENTICATION_FAILED (0XC00002C3). It shows up in event logs as Event ID 4 from source Kerberos. I've seen this most often when a computer's AD account gets corrupted — maybe someone deleted it by accident, or a domain controller restore created a mismatch. Another common trigger: you're trying to access a service like SQL Server or IIS from a remote machine, and the service principal name (SPN) is missing or duplicated.
Root Cause: Broken Trust or Missing SPN
Kerberos works like a handshake. When your computer requests a ticket to access another system (say a file server), the domain controller checks two things: first, that your computer account is valid and has a matching secret (password), and second, that the target service has a proper SPN registered. If either side fails to prove its identity, you get this error. The most common scenario I've seen: a client's laptop was removed from the domain to fix something else, then re-joined with the same name — but the old computer account still had a different password hash. The DC sees the mismatch and refuses the mutual authentication.
Fix Step by Step
Step 1: Verify the Computer Account Exists in AD
Log into a domain controller or use Remote Server Administration Tools. Open Active Directory Users and Computers. Find the computer object. If it's missing, you need to rejoin the domain. If it's present but disabled (grey arrow), enable it.
Step 2: Reset the Computer Account (Most Common Fix)
Do this from an elevated PowerShell on the affected machine:
Reset-ComputerMachinePassword -Server <DC Name> -Credential (Get-Credential)Replace <DC Name> with an actual domain controller. Enter domain admin credentials when prompted. This forces the machine to regenerate its password and push it to AD. After the command succeeds, reboot the machine.
Step 3: Check the SPN for the Target Service
If the error appears when accessing a specific service (like SQL, Exchange, or a web app), run this from a domain controller to see if the SPN exists and is unique:
setspn -Q <service>/<hostname>For example: setspn -Q MSSQLSvc/sqlserver01.contoso.com. If you see multiple entries for the same SPN, remove the duplicates. If it's missing, register it:
setspn -A <service>/<hostname> <computeraccount>Step 4: Clear Kerberos Tickets on the Client
On the failing machine, open an admin command prompt and run:
klist purgeThen reboot. This flushes any cached bad tickets. If you're in a hurry, you can also run ipconfig /flushdns to clear DNS cache, though that's rarely the culprit here.
When the Fix Doesn't Work
If the error persists after resetting the computer account and checking SPNs, look at DNS. Had a client whose entire print queue died because the domain controller had a stale A record pointing to an old IP. Run nslookup <FQDN of DC> from the affected machine — make sure it resolves to a live domain controller. Also, check the system time: Kerberos requires time sync within 5 minutes. Run w32tm /query /status to confirm the machine is syncing with the domain. If all else fails, leave the domain and rejoin — but back up any local profiles first or they'll get orphaned.
One more thing: if this is happening to multiple machines at once, your domain controllers might be out of sync. Check AD replication with
repadmin /replsummary. Broken replication can cause account password mismatches across sites.