DllImport Problem

Hi everybody!
i'm new in CE and i've got a problem with DllImport.
when i write this code:
//=======================================================
[DllImport("coredll.dll", SetLastError = true)]
[return: MarshalAs(UnmanagedType.Bool)]
private static extern bool EventModify(IntPtr hEvent,
[In,MarshalAs(UnmanagedType.U4)] int dEvent);
//=======================================================
i got this error
The Type or namespace name 'DllImport' could not be found (are you missing
a using directive or an assembly reference?)

whats wrong with it?

Add to the using part of your code.
using System.Runtime.InteropServices;