Pointer not set for location referenced.

["Eric Wolf" <eric_a_wolf@xxxxxxxxxxx>]

  To the list,
  I have looked through the archives but cannot seem to find an explanation
  for what is occuring.  Here it is:
   
  My users are receiving this error MCH3601 Pointer not set for location
  referenced on different programs during the day.  All the programs are
  using modules of a service program to retrieve a single record from a
  file.  Each module is being passed the external datastructure of the file
  to be retrieved and the datastructure is being cleared and the key fields
  are being reset before each execution of the module.  They pretty much all
  look something like this:
   
  /free
  ...
  clear carrier;
  carrier.id = ordcarrier;
  carrier = RtvCarrier (carrier);
  ...
  /end-free
  Every once-in-a-while, the error appears when attempting to execute the
  RTVCARRIER statement. After receiving the error message, the users sign
  off and back on again and all is fine.  None of the modules have changed
  and new modules are added to the end of the SRVSRC BND
  member. The programs that are "calling" the modules are compiled with the
  ACTGRP(*CALLER) 
   
  Any suggestions as to where to focus my attention would be greatly
  appreciated...
   
  TIA,
  Eric A. Wolf