Error 1 The type 'System.Tuple' exists in both 'c:\Program Files (x86)\Reference Assemblies\Microsoft\Framework.NETFramework\v4.0\mscorlib.dll' and 'c:\Program Files (x86)\FSharp-2.0.0.0\bin\FSharp.Core.dll' C:\Users\Bent\documents\visual studio 2010\Projects\FSharpExtensionsCSharp\FSharpExtensionsCSharp\FSharpListEx.cs 51 41 FSharpExtensionsCSharp
It looks like you're trying to use a 2.0/3.0/3.5 framework version of FSharp with 4.0. If you change your projects to target 3.5 or 3.0 or 2.0 etc. you should be fine.