Possible Duplicate:
Including FSharp.Core in a C# project: resolving type collisions
I have referenced the Microsoft.FSharp.Core.dll file to my web application on .NET.
My fsharp function returns to C# a
Tuple<string,int>
It marks in red in C#
Tuple<string,int>
saying that it exists in the library FSharp.Core.dll and mscorlib.dll
Is there a way to specify that its a FSharp tuple or vice versa?
Are you using .NET 2.0 (or one the other frameworks build on .NET 2.0 like .NET 3.0 or .NET 3.5) or .NET 4.0?
.NET 2.0 does not include a tuple definition so the version of F# compatible with .NET 2.0 ships with it’s own definition for a tuple. In this case you need to reference FSharp.Core.dll and open System and you the Tuple<> class should be in scope.
.NET 4.0 includes a definition of Tuple<> in mscorlib.dll and this is the tuple definition that the version of F# that ships with VS2010 uses, in this case it should not be necessary to reference FSharp.Core.dll. Deleting the reference to FSharp.Core.dll should solve your problem.