using System.Runtime.InteropServices;

[ComImport]
[Guid("09133803-EF59-4467-9135-255A65B606C2")]
interface IA
{
    void Foo(ref int x);    
    void Foo(ref long y);    
}

class A : IA
{
    private static void Main()
    {
        IA x = new A();
        x.Foo(1); // error CS0121: The call is ambiguous between the following methods or properties: 'IA.Foo(ref int)' and 'IA.Foo(ref long)'
    }

    public void Foo(ref int x)
    {
    }

    public void Foo(ref long y)
    {
    }
}