Have you tried installing the correct W7 root certificates? You can download it from the MS Update Catalog. If this will be your first time to go to MUC, it will ask you to install the active-x, allow it, then do a search of KB931125. Download the appropriate certs for W7, unzip it then manualy install the root certs by running the executable(exe).
»catalog.update.microsoft.com/v7/ ··· ome.aspx