The code you are looking for may be within mimsbatch.pl look for ERR_ABORT and ERR_CONT,
however I do not seem to understand from your description what you are trying to achieve, maybe you wish to post a copy of you batch task entries.
If you have a PRESENT sub-task to check for the existence of a file, it does not make sense to attach "-error" in the sense you describe, because this negates the purpose of PRESENT which is exactly to stop further processing if a file does not exist; If you wish to continue with processing regardless, you do not need a PRESENT sub-task.
But maybe your interpretation of NEXT is incorrect?
My documentation states that:
"NEXT" is the default behaviour, which means that if an error occurs in a subtask-the rest of the task is ended, and processing continues with the NEXT task NOT SUBTASK. Therefore you do NOT need to code for -error NEXT explicitely, this is the default.
ABORT is a stream control and will abort the ENTIRE stream (Update, report, online) - so use carefully
CONTINUE is probably what you are after, it means that if a sub-task aborted, it will not cause the task to end, processing continues with next sub-task within the task.
However it does not make sense to use PRESENT with - error continue, as explained.