Outlook and Exchange 2007 Issues

OK I'll spring this one out here. We did a transition from Exchange 2003 to 2007, the old 2003 has been retired. Clients can use the OWA to access their email, but any users who want to use Outlook 2003/2007 get the following message

The connection to Microsoft Exchange is unavailable. Outlook must be on line or connected to complete this action

Any ideas?

Try running

outlook /rpcdiag

and double check that the client is connecting to the correct server using the correct protocol.

Ahh sorted it. I think ...

I did try that, it was something really odd with the global catalogue server.