I've got an odd issue here. A client is trying to connect to Exchange in cache mode over VPN via his laptop and PDA. He used to be able to do so fine, but for some reason, without any changes being made to his system or configuration, he hasn't been able to anymore this last week. He receives the message "the server is not available".

I'm new to Exchange, so I'm rather lost on this one. Can anyone point me in a direction to get started with on this issue?