Whs Shares Behind Nat

I have been using a WHS since 2007 but recently i had to add a pc to my home network that doesn't have a wireless card (no room in pci slots). In the same room I had an ovislink AP running in wisp mode with my router giving internet access to something else and as the AP has two ethernet ports i connected the new pc and it has internet access as well but cannot see my whs shares although the whs connector on the new pc runs fine and takes back-ups of my installation.
I get a message that whs shares are not available behind a nat.

Any suggestions to fix this? (and no, i don't want to buy a usb wi-fi)