My Extensions ??

This functions as a C3 program in LINQPad4

void Main()
{
	var t = new Dictionary();
	t.GetType().Implements().Dump();
}

// Define other methods and classes here
public static class TTTT
{
	public static bool Implements(this Type type) where TInterface : class 
	{
		var interfaceType = typeof(TInterface);

		//if (!interfaceType.IsInterface) { throw new InvalidOperationException("Only interfaces can be implemented."); }

		return (interfaceType.IsAssignableFrom(type));
	}

}

But if i move the extension to "My Extensions" (other extensionmethods deleted for abbrevity):

public static class MyExtensions
{
	// Write custom extension methods here. They will be available to all queries.
	public static bool Implements(this Type type) where TInterface : class 
	{
		var interfaceType = typeof(TInterface);

		if (!interfaceType.IsInterface) { throw new InvalidOperationException("Only interfaces can be implemented."); }

		return (interfaceType.IsAssignableFrom(type));
	}

}

I get the error message:
"'System.Type' does not contain a definition for 'Implements' and no extension method 'Implements' accepting a first argument of type 'System.Type' could be found (press F4 to add a using directive or assembly reference)"

Am i doing something wrong?