MN-500 MS Exchange Error in Outlook on VPN

I have a MN-500 that I connect straight to my cable
modem; from there I have several computers wired to it as
well as three wireless computers on my network. One of
these wireless computers is my company laptop with a MN-
520 adapter. I use a VPN connection to access company
resources; one is email through MS Exchange Server using
Outlook. This function was working great until a few
months ago and I made no changes to my network that I
know of. Now I get an error when using wireless adapter
or even hard wired to the router -

Outlook Send/Receive Progress Error

Task 'Microsoft Exchange Server - Sending and Receiving'
reported error (0x8004011D) : 'The server is not
available. Contact your administrator if this condition
persists.'

I'm getting tired of having to take my entire network
down to plug straight in my cable modem to syncronize my
company email.

Any suggestions would be greatly appreciated.