Hello @Ming Cheung
Thank you for posting here.
We can try to request acertificate based on the steps in the following link, then check if we can request certificate successfully.
https://learn.microsoft.com/en-us/answers/questions/89382/unable-to-sign-csr-with-microsoft-windows-ca.html
If is does not work, either. Would you please tell us
1.When we encountered the error message above?
2.Did you receive the error message above when you click submit button?
3.What certificate template do you use?
4.The detailed steps you are operating?
For example:
1.Create certificate template and grant the permissions.
2.Issue certificate template on CA server.
.........
Best Regards,
Daisy Zhou