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>My BO code is in VS 2010 Pro but I had to use VS 12013 Express to get the example to work. Is it possible to use my existing BO dlls from VS 2013?
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Assuming you are using WebAPI 2, it will be using .NET 4.5 (or 4.5.x). MM.Net for 2010 should be using .NET 4. You should be able to reference your BO dlls as .NET 4.5 extends/replaces .NET 4.