You can’t edit a TFS 2010 build workflow template with just Team Explorer installed
I tried to open a TFS 2010 build template within the Visual Studio shell (the bit that gets installed when you put Team Explorer onto a PC) and saw the error “The document contains errors that must be fixed before the designer can be loaded”.
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At the bottom of the screen it showed that all the underling assemblies could not be found.
The solution is simple, install a ‘real version’ of Visual Studio, I put on Premium. It seems that the shell does not provide all the assemblies that are needed. Once I did this I could edit the XAML with no problems
Read the complete post at http://blogs.blackmarble.co.uk/blogs/rfennell/archive/2010/11/12/you-can-t-edit-a-tfs-2010-build-workflow-template-with-just-team-explorer-installed.aspx