Get Ambiguous method with enum parameters

I'm trying to invoke a method from a dynamically loaded assembly. The method is ambiguous.

For example: The dll contains the following methods:

public static string ReadString(string key, KeyType type)
public static string ReadString(string key, string type)

I would like to invoke the one with the enum parameter KeyType.

var assembly = Assembly.LoadFile(@"stringutils.dll");
Type type = assembly.GetType("Utils.StringReader");

I tried

var method = type.GetMethod("ReadString", new[] { typeof(string) });

And tried

var method = type.GetMethod("ReadString", new[] { typeof(string), typeof(int) });

But it returns null