CFB

Explanation
One of the following occurred: During JES3 initialization, JES3 could not attach the JES3 auxiliary
task, module IATAUX. ATTACH processing writes message IAT3005 to the
console.
After JES3 initialization, the JES3 auxiliary task, module IATAUX,
could not recover from an error and abnormally ended. The ESTAI routine
in module IATABMN requests a dump of module IATAUX to the SYSABEND
or SYSUDUMP data set.

System action
JES3 ends.

System programmer response
If module IATAUX could not be attached,
the system issues messages about the job. Make sure that the failing
job step includes a SYSABEND statement.
Collect all printed
output and output data sets related to the problem. If the problem
occurs in JES3 you should: Obtain system dump by specifying DUMP=JES on the OPTIONS card
in the initialization deck and save the output
Provide a console log from initialization
Provide a listing of the JES3 start up procedure, containing all
JCL used to start the subsystem.

If module IATAUX abnormally ended, the system sends messages
about the job to one of the following: The primary console
The remote console, for a system with remote consoles
The hard-copy log for a system with multiple console support (MCS)

 Make sure that the failing job step includes a SYSABEND statement.
Collect
all printed output and output data sets related to the problem.

Programmer response
If JES3 wrote message IAT3005 to the console,
make sure that module IATAUX is in one of the following: The library concatenation defined by the JES3LIB initialization
statements, if used.
The STEPLIB concatenation defined in the JES3 procedure.
The linklist specified in response to message IEA101A.

If JES3 did not write message IAT3005, look in the dump
of module IATAUX to find the system completion code for the module's
failure.  Respond to that completion code.

Source
JES3