Getting error Security Authority cannot be contacted while using Kerberos

[Engr]

We have a server on which we are using Kerberos security. We have disabled
NTLM. When we try to access, we get the error 'Security Authority cannot be
contacted'.

We have created a virtual directory. Then we created an app pool. Then we
assigned a domain user to the pool. And added SPN entry for the server and
the domain user.

This is working on one computer but not on another. Both are in the same
domain.

Any clues?