Error compiling a VS .net solution

[nbufkin]

I am getting an error compiling a vs .net solution file from Visual Build. This error message is not repeated when I open .sln and compile it from the ide.

Item has already been added. Key in dictionary: "CD706663-93B3-4879-B469-95D198D64E41" Key being added: "CD706663-93B3-4879-B469-95D198D64E41"
Step 'Compile Aim.sln' failed
Build ended.

Any suggestions? I checked the registry for a class id named CD706663-93B3-4879-B469-95D198D64E41 and came up with nothing