CERT, OAB, OOF and Schedule Free/Busy

Hi,

I have a real strange issue.

I have 1500 users running on Exchange 2010 for the past 2 years.

We have 2 CAS/HUB server’s load balanced with Windows NLB and 2 MB servers with a DAG.

CERTS are valid until the end of this year.

Now my problem is that ONE user running Outlook 2010 reported a Cert error - "The name on the security cert is invalid or does not match the name of the site"

And because of this the user cannot download the OAB, set OOF or view Schedule Free/Busy.

I have checked AutoDiscoverServiceInternalUri and it is not pointing to any individual CAS servers.

When I run Test E-mail Autoconfiguration it reports “Autoconfiguration was unable to determine your settings”

I have tried recreating the Outlook profile and also creating on a different PC but same results.

As mention all is working fine for all other users.