ATPLoad
ATPLoad first checks whether the .MPP driver is already loaded and running. If it is not, ATPLoad verifies that port B is configured for AppleTalk and is not in use, and loads MPP into the system heap. ATPLoad then loads the .ATP driver, unless it's already in memory. On a Macintosh 128K, ATPLoad reads the .ATP driver from the system resource file into the application heap;
on any Macintosh later than the 128K, ATP is read into the system heap.
portInUse (-97) Port B is already in use
portNotCf (-98) Port B not configured for AppleTalk
Notes: On any Macintosh later than the 128K, ATPLoad and MPPOpen perform essentially the same function.