system.diagnostics.contracts.contract exists in both v4.0 v3.5

I just upgraded to visual studio 2010 and installed the code contracts msi. When I try to use it I get a compiler error that the system.diagnostics.contracts.contract dll exists in both the v3.5 and v4 framework. Anyone k开发者_如何学运维now what I should do to resolve this? Thanks.

If you're upgrading a .NET 3.5 project that uses contracts to .NET 4.0, make sure you remove your reference to the Microsoft.Contracts assembly.

The Microsoft.Contracts assembly provides code contracts for use in .NET 2.0 or 3.5 projects, but is provided by default with .NET 4.0 in mscorlib, so you don't need it. They both share the System.Diagnostics.Contracts namespace, so by having references to both at the same time, the compiler isn't able to figure out which one you're trying to use.

I solved it by first installing it, thou that did not actually solve it. Then removed the references and then I changed the project versions to 4.5 and after that, it worked.