500

Explanation
During processing of an I/O request, execute channel
program (EXCP) processing encountered an error while validating a
control block. Each X'500' abend code has a reason code that
explains the error: Code
Explanation
1
The IOBM field of an Indexed Sequential Access Method (ISAM) input/output
block (IOB) specified an extent of zero.
2
A data extent block (DEB) points to a unit control block (UCB)
that is not valid. The third byte of the UCB did not contain X'FF',
as required.
3
The IOBEID field of the Input/output block extension (IOBE) control
block does not contain the characters &lsquo;IOBE&rsquo;,
which is required.
4
The version field of the IOBE is not compatible with the IOBEVRSC
version label. The version field must equal the IOBEVRSC version label.
5
The IEDBID field of the I/O error data block (IEDB) control block
does not contain the characters &lsquo;IEDB&rsquo;, which
is required.
6
The version field of the IEDB is not compatible with the IEDBVRSC
version label. The version field must equal the IEDBVRSC version label.

System action
The system abnormally ends the current task and
issues a SNAP dump.

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 databases
for a fix for the problem. If no fix exists, contact the IBM® Support Center. Provide the JCL and the SNAP
dump.

Programmer response
Correct the problem that the reason code
indicates. Ensure also that the problem program correctly built or
modified the control blocks. If the program is correct, the problem
is a system problem.  Run the job again, requesting an ABEND dump.
 Notify the system programmer.

Source
Execute channel program (EXCP)