Alsys DOS question

[tim@trident.datasys.swri.edu (Timothy J. Barton)]

Howdy.  I am writing an Ada application using the Alsys ver. 5.1 DOS 32-bit
compiler.  I need to catch DOS "critical I/O errors" so the infamous
"Abort, Retry, Ignore, Fail" message doesn't blast itself into the middle of
my pretty application when the user tries to print to a nonexistent LPT2.

I have a routine that opens the hardware port, and I think I have made the
proper calls to catch the critical I/O error, but I have been unable to 
stop the message from going to the screen.

Thanks for everyone's suggestions to my previous exception handler question.
Special thanks to the guys (and gals) from Verdix.

Any suggestions?  Code looks like the following:
-------------------------------------------------------------------------

  function OpenPrinter return BOOLEAN is
  begin
    DOSE.Critical_Error_Set;    --  Should install INT24 handler

    OPEN( FILE => prnFile,
          MODE => OUT_FILE,
          NAME => "lpt2" );

    DOSE.Critical_Error_Reset;  -- Should restore default INT24 handler
    return TRUE;

  exception
    when others => DOSE.Critical_Error_Reset;
                   return FALSE;
  end OpenPrinter;

----------------------------------------------------------------------------
Timothy J. Barton                         tim@trident.datasys.swri.edu
Senior Research Analyst                   (210) 522-3540
Southwest Research Institute (SwRI)       (210) 522-5499  (Fax)   
San Antonio, Texas  78228-0510