access Exchange over a wireless router

At my home office I connect via VPN to our corporate network. When I am hardwired to the router I can access everything including my Exchange mailbox. However, when I am connected over wireless, I can still access my corporate LAN but I cannot get access to my Exchange Mailbox. I get a dialogue window telling me Outlook is retrieving data and it takes forever and eventually times out. Anyone have a solution? Is there something I have to configure on the router?