During the deployment testing of an integration component with Commerce Server 2009’s Order Service I encountered the following error at a client site "Column requires a valid DataType." It was occuring right at the point when deserializing the dataset from the GetPurchaseOrderAsDataSet() call. We did not encounter this problem at all on any of the workstations. The call stack was essentially of no help. After some usage of FileMon and a few other diagnostics tools it struck me that maybe there was some crazy framework reflection work going on behind the scenes and it was attempting to load a soft dependency during the deserialization. After thinking about it, I realized that it must depend on some of the Commerce Server types. I installed the Order Management client tool that comes with Commerce Server and it all went away. The client was fine with installing this on the production integration server so we left it at that. I am sure that you could find a way to minimize what is necessary for deployment, but this is how we decided to quickly resolve the issue. Voila, we’re all fixed!