To fix this error, the following code can be added In the SARSTCUX exit:
IEZIOB , MVS Input/Output Block
IOBDSECT EQU IOBSTDRD,0,C'J' Start of I/O Block DSECT
IOBLENG EQU IOBEXTEN-IOBSTDRD+L'IOBSEEK Length of IOB
Or they can use the JES2 $MODULE MACRO and specify $BUFFER with it, like this:
$MODULE TITLE='JES2 Macros',
+ $BUFFER
Note: The $MODULE MACRO contains code that will include IEZIOB and generate the above equates automatically.
After adding the above code assemble completed successfully.