Mismatched Address. Certificate issues

I have a strange issue I am hoping someone can help me solve.

Basically I run SBS2011 (Exchange 2010). I have a self signed certificate that works fine for all existing clients and myself. (using OWA or http over RPC). My Outlook client connects with no problem at all, I use it daily as do some of the consultants that work for us.

I have tried connecting new user up via Outlook over RPC, or a existing user on a new PC (off site) and I get the mismatched Address error. It seems to be the same certificate used as the PC's that are working.

I also get some strange results from the test connectivity.

It is failing on the Certificate, Certificate trust is being validated, Attempting each method of contacting the Autodiscover service

Any help will be appreciated, one of the messages is below, don't understand how a few work and some don't??

	Certificate trust is being validated.
	Certificate trust validation failed.
	Test Steps   The Microsoft Connectivity Analyzer is attempting to build certificate chains for certificate CN=xxxx.co.uk, OU=xxxx, O=xxxx, L=xxxxxx, S=xxxxxxx, C=GB.   A certificate chain couldn't be constructed for the certificate.   Additional Details   The certificate chain couldn't be built. You may be missing required intermediate certificates. Elapsed Time: 34 ms.