Automatic upgrade of Plugins not working on Windows Server 2008

I have installed WordPress on our hosting system Web.com which we are using Windows Server 2008 and IIS 7. I have it working fine but when I try to use automatic upgrade of a plugin that says one is available, I click to proceed, it then asks for FTP address, user-id and password, which I supply and hit proceed. It then processes for awhile then comes back with the upgrade screen but the content area is blank and no upgrade occurred. Any help on this?