Troubleshooting Active Directory certificate authentication issues can often be a complex and difficult process. Here are some steps you can take to help you resolve the issue:

1. Step 1: Check that the correct version of the client certificate is installed.
2. Step 2: Verify that the server is accepting the client certificate.
3. Step 3: Check that the server is resolving the DNS name of the client certificate.
4. Step 4: Check that the client credential is valid and has not expired.
5. Step 5: Verify that the certificate is registered on the domain controller.
6. Step 6: Check that the certificate has the correct permissions set on the server.
7. Step 7: Check the group policy settings and make sure they are correct.