I was facing an error while creating site using SharePoint Commerce Services Wizard after installing Commerce Server Template pack for SharePoint 2010. Site provision was failing with an error like
cannot add the specified assembly to the global assembly cache: Microsoft.Commerce.Portal.UI.Orders.dll
Solution which I got after some search on web is that go to GAC / assembly folder and find these assemblies and uninstall manually, after this you should re-try creating the sites using CSC wizard
This worked for me and hope helps some one J