newbie prototype question...

I am trying to execute a simple prototype program but I keep getting an
error(it compiles fine). I am calling the program as follows:

CALL PGM(MYLIB/PROTO) PARM(1 2)

There might be a very simple mistake I am doing..I am also looking for a
very simple example on a subroutine program and a program which uses /COPY.
Any help in this matter will be greatly appreciated.

     D addnums         PR                  EXTPGM('PROTO')
     D  num1                          1  0
     D  num2                          1  0

     D addnums         PI
     D  num1                          1  0
     D  num2                          1  0


     D  num3           S              1  0

      /free
         num3 = num1 + num2;
         dsply num3;
         dsply 'DONE';
         *inlr = *on;
      /end-free

Error:

D
Pointer or parameter error (C G D F).

Thanks in advance,

Jake.