Error occurred in the COBOL program.

Hello List,

This may be a COBOL newbie question, but....

Our organization has a set of COBOL programs that has been running 
successfully for approximately 20 years (yep, 20!).  In the last two 
months, we have twice received the following messages and I cannot seem to 
track down what is wrong:

Error at statement 1558 instruction 05CE. 
Cause . . . . . :   An error occurred in the COBOL program.  The COBOL  
  statement and/or the MI instruction where the error occurred is given in 
the
  message text.  Another message will be issued following this message. 
Refer 
  to the COBOL statement or MI instruction for the recovery procedure.  
Recovery  . . . :   If a COBOL statement number is not given the MI  
  instruction number can be used to determine which source statement  
  encountered the error.  An MI listing of the program can be obtained by  
 
  recompiling using the CRTS36CBL command with the generation option 
*LIST. 

CBL3035 Options (0 23F) 
 
I/O operation failed. Required error handler missing.
Cause . . . . . :   A return code received from an Input-Output operation  
 
  cannot be properly identified by the error handler.  
Recovery  . . . :   Enter 0 to continue running, 2 to cancel job step, or 
3 to
  cancel job.  
Possible choices for replying to message . . . . . . . . . . . . . . . :   

  0 -- The program is continued.  
  2 -- The program is ended.  Any data created up to this point is saved, 
and 
    the job continues with the next job step.  
  3 -- The program and the job are canceled.  Data created by previous 
steps 
    in this job is saved and data created by this program is lost.  
  D -- Same as option 3, but a job process dump is produced.  
 F -- Same as option 3, but a COBOL formatted dump is produced.

The message was answered with a 3 before I was notified, so I couldn't get 
a dump or look at the invocation stack.  I'm not sure which program is 
giving the message since the messages don't indicate the program name 
(even with F9=Display message details).  The first message ID is CBL3018. 
The other two are CBL3035.  I have searched the IBM site and the web for 
these message ID's and have found absolutely nothing.

Any clues would be most appreciated!