Intercept messages from USB auxiliary device

[cuitino]

I was attempting this with a bar code scanner input device, which operates like a keyboard. 
However I am getting the error:

System.AccessViolationException: Attempted to read or write protected memory. This is often an indication that other memory is corrupt.
   at line 42 in Raw input.cs, Program.<<Main>$>g___WmInput|0_0(IntPtr wParam, IntPtr lParam)
   at line 15 in Raw input.cs
   >>

line 42 points to 
    print.it(data,8);
line 15 points to:
    if (m.message == api.WM_INPUT) _WmInput(m.wParam, m.lParam);