300

Explanation
During processing of an I/O request, execute channel
program (EXCP) processing encountered an error. Each X'300' abend
code has a reason code that explains the error: Code
Explanation
1 - 2
EXCP encountered an incorrect data extent block (DEB) at one of
the following phases during the validity check: Reason code 1 - front end processing
Reason code 2 - while processing a related request (RRQE)

 The problem can be one of the following: The DEB does not exist in the DEB TABLE.
The offset in the DEB TABLE (DEBTBLOF) for this DEB is less than
1 or greater than the number of entries in the DEB TABLE.
The DEB address that was obtained from the data control block
(DCB) does not match any entry in the DEB TABLE.

3
The DEB is not an EXCP or Indexed Sequential Access Method (ISAM)
DEB.
4
The system detected that the IOBM field in the input/output block
(IOB) is higher than the maximum extent count (DEBNMEXT) in the DEB.
5
The Related Request Queue (RRQ) address in the DEB does not match
the RRQ address in each Request Queue  Element (RQE) associated with
the DEB.
6
Dataset Name Hiding is active and the user does not have RACF/SAF
Facility Class Authorization to read the VTOC.
7
During EXCP purge processing an invalid input/output block (IOB)
was found on the IOB restore chain.
8
During EXCP purge processing, an invalid DEB
was found in the job step TCB's DEB table.

System action
The system abnormally ends the current task and
issues a SNAP dump.
For reason code 8, the system records the
condition and continues processing.

System programmer response
  In the dump, look at field TCBEXCPD
at offset X'C0' in the task control block (TCB) for the current
task.  TCBEXCPD points to the EXCP debugging area (XDBA). The XDBA
contains diagnostic data associated with the EXCP processor.
If
the error recurs and the program is not in error, look at the messages
in the job log for more information. Search problem reporting data
bases for a fix for the problem. If no fix exists, contact the IBM® Support Center. Provide the
JCL for the job and the dump.

Programmer response
Correct the problem that the reason code
indicates. Verify that the DCB contains the address of the DEB. Correct
the error. Run the job again.
 For reason code 6, obtain read
access to the 'STGADMIN.IFG.READVTOC.volser' Facility Class profile
and rerun the job.
For reason code 8, this condition usually
occurs following some other task terminating condition (for example,
an out of storage condition). Correct the task terminating condition
and run the job again. Note that this condition is recorded only (no
dump is taken). The system continues purge processing.
If the
error recurs, check the problem program for the error. If the error
cannot be determined, run the job again, requesting an ABEND dump.
 Notify the system programmer.

Source
Execute channel program (EXCP)
For reason code
5, also EXCP purge exit IECVEXPR.
For reason code 7, IECVEXPR.

For reason code 8, IECVEXPR.