Win32 API bug

Code:

---

                [DllImport("user32")]
                public static extern int GetClassName(
                        int hWnd,
                        string lpClassName,
                        int nMaxCount
                        );

---

I am just messing around trying to refresh my memory on some stuff I haven't done lately. Right ow I am making a simple Window Info Spy to get some practice using the Win32 API. The problem is that I can't this to pass out a value. If I add ref or out to string lpClassName I get a fatal crash. With out the out/ref mark I get nothing.

Anyone know what might be doing this xor how to fix it?

Code:

---

                [DllImport("user32")]
                public static extern int GetClassName(
                        int hWnd,
                        [MarshalAs(UnmanagedType.LPTStr)]
                        string lpClassName,
                        int nMaxCount
                        );

---

Now I have a string that is in an unreadable format.....