Errors with Methods and Classes ( Threading )

C# 4.0 using SharpDevelop

These are the errors I get with the following program.

in Program.cs Line 21 Error = Argument1:cannot convert from 'void' to 'System.Action' (CS1503)
in Program.cs Line 21 Error = The best overloaded method match for 'voidoverrideproblem.ThreadClass1.SeparateThread(System.Action)' has some invalid arguments (CS1502)

Its three files. Each one is named with the source code to it.

Uncomment ( // ) one of the two choices in the Program.cs file to see the problem. One works, the other does not. The one that does not work is the one I need to solve the answer too.

I just cannot seem to figure out how to solve this so that it works. Anyone have any ideas on this ?

// Program.cs
using System;

namespace voidoverrideproblem
{
 class Program
 {
 public static void Main(string[] args)
 {
 string thenumber = "25565";
 
 DisplayTheNumber runnumber = new DisplayTheNumber();
 
 ThreadClass1 startthread = new ThreadClass1();

 // Choice 1 here works.
 // runnumber.DisplayNumber(thenumber);

 // Choice 2 does not.
 startthread.SeparateThread(runnumber.DisplayNumber(thenumber));
 
 Console.Write("Hit any key to exit.");
 Console.ReadKey();
 }
 }
}


// ThreadClass1.cs
using System;
using System.Threading;

namespace voidoverrideproblem
{
 public class ThreadClass1
 {
 public void SeparateThread(Action action)
 {
 var thread = new Thread(new ThreadStart(action));
 thread.Start();
 }
 }
}




// MainMenu.cs
using System;

namespace voidoverrideproblem
{
 public class DisplayTheNumber
 {
 public void DisplayNumber(string thenumber)
 {
 Console.WriteLine("The current port is : " + thenumber);
 }
 }
}