Comment Attachment Processing compile error

I'm trying to do something that should be very simple - determine the existence of Comments on Invoice Messages, just like MA66 does when it needs to determine what text to put in the Message Button on the screen.  Simple, no?

I looked through the API manual to see if there was any voodoo involved - looked pretty easy. copied the code right out of MA66PD and dropped it into my program.

             INITIALIZE                 WS-CMTMAG.
             MOVE SPACES             TO CMTMAG-TYPE.
             SET CMTMAG-KFIND        TO TRUE.
             PERFORM 900-FIND-BEGRNG-CMT-MAINVMSG.
             IF (CMTMAG-KFOUND)
                 MOVE 908                TO CRT-MSG-NBR
             END-IF.

Failures all over the place:

 43198     INITIALIZE                 WS-CMTMAG.
*  12-S****************************************                              **
**    Operand WS-CMTMAG is not declared
 43199     MOVE SPACES             TO CMTMAG-TYPE.
*  12-S******************************************                            **
**    Operand CMTMAG-TYPE is not declared
 43200     SET CMTMAG-KFIND        TO TRUE.
*  12-S********************                                                  **
**    Operand CMTMAG-KFIND is not declared
 43202     IF (CMTMAG-KFOUND)
*  12-S*********************                                                 **
**    Operand CMTMAG-KFOUND is not declared

On the surface, it looks like the library that contains these members is not getting linked in, but that should happen automatically based on the existence of PERFORM 900-FIND-BEGRNG-CMT-MAINVMSG in my PD - or have I completely misunderstood how this should work? (Or, is there something else that my program needs to contain to cause the library to be automatically linked?)