CS0305, Invalid number of arguments when using System.Func delegate

I get following error:

error CS0305: Using the generic type 
'System.Func<T1,T2,T3,T4,T5,T6,T7,T8,T9,TResult>' 
requires '10' type arguments

On this line:

public static IDoubleArray ApplyFunc(IDoubleArray inputArray1, 
                          IDoubleArray inputArray2, 
                           Func<double, double, double> f) {

The Func definition in the System namespace looks like this:

[TypeForwardedFrom("System.Core, Version=3.5.0.0, 
                    Culture=Neutral,      
                    PublicKeyToken=b77a5c561934e089")]
public delegate TResult 
       Func<in T1, in T2, out TResult>(T1 arg1, T开发者_如何学Go2 arg2);

Everything looks fine, but compiler doesn't think so.

Any ideas how to solve this?

Thanks.

edit:

The call looks like this:

/// <summary>Inverse cumulative distribution function</summary> 
        /// <param name="p">Probabilities at which to compute the inverse cdf</param>
        /// <param name="mu">Scale parameters</param>
        public static IDoubleArray Inv(IDoubleArray p, IDoubleArray mu)
        {
            return ArrayMath.ApplyFunc(Matrix.ConvertToMatrix(p), Matrix.ConvertToMatrix(mu), Inv);
        }

Solved. The problem was the target wasn't .NET 4.0.