The IOF "COMTRACE" command can be used to get additional information about the error. This additional information should point to the parm(s) that are incorrectly or incompletely defined. To use:

• Enter the "COMTRACE ON" command to enable communications tracing.
• Enter the "AT" command.
• If an APPC session is actually started, end it and return to the original IOF session.
• Enter the "COMTRACE OFF" command to disable communications tracing.
• The trace is recorded in the Job Console Log of your TSO session, and in the system log (SYSLOG or OPERLOG).
• Select your TSO session, and then select data set number 1, your Job Console Log.

   1) Allocate a PS dataset.  DCB characteristics don't matter unless
      you specify a BLKSIZE.  If you do, make it 4096.  The other DCB
      characteristics will be overwritten.  Best way to do this is to
      issue these commands from TSO READY or ISPF Option 6:

         ALLOC FILE(X) DA(...dsn...) NEW CAT TRACKS SPA(15) DSORG(PS)
         FREE  FILE(X)

      This will allocate a dataset with no DCB characteristics.  Be
      sure to specify enough space for the trace.  There is no point
      in specifying secondary space.  APPC will only use the primary
      space allocation wrapping back to the front when it hits the
      end of the primary space.

   2) Make sure that the client address space and the server address
      space have UPDATE access to the trace dataset.  The client is
      the TSO session that initiates the IOF session.  The server is
      the transaction processor address space which is initiated when
      the AT command is issued.  Both should normally have the same
      userid environment, so as long as the TSO session can update the
      dataset, the server should be ok also.

      Additionally, the APPC address space also needs access to the
      dataset.  If this is a RACF system, then this should occur
      automatically.  If not RACF, then you might have to do something
      to set this up.

   3) Issue the Rexx exec ATBTRACE with the following parms:

        ATBTRACE START DA(Step #1 DSN) LU(partner_LU) TP(APPC_TP_name)

      Basically, the partner_LU is the LU name defined in the B67
      option member and APPCTP_name is the transaction processor
      name define in B67.  You can also add the USERID parameter to
      filter the tracing down to APPC sessions that involve that userid.
      The syntax of the USERID parameter is as follows:

             USERID(userid)

      ATBTRACE causes APPC to trace the side of the conversation that
      is on this CPU.  If both sides of the conversation are on the
      same CPU, then you will see both sides of the conversation.

      Also, it appears that to capture a trace, you need to issue the
      ATBTRACE command prior to initiating the APPC session.  You can't
      get into an APPC session and then start tracing.

   4) Run the APPC function to be traced.

   5) Issue the Rexx exec ATBTRACE with the following parms:

        ATBTRACE STOP DA(Step #1 DSN)

   6) Read the dataset, it is in text format.