RNQ0121: Array index not valid

What it means

RNQ0121 is an ILE RPG runtime message for program status 00121, which IBM's ILE RPG Reference lists as an array index that isn't valid. RPG arrays start at element 1 and end at the number given in DIM. Every time the program reads or changes an element, the runtime checks the index. An index of 0, a negative index, or one above the DIM value raises the error. The help text names the array.

A multiple-occurrence data structure has its own status. Setting an occurrence outside its range is status 00122, not 00121.

RNQ0121 is the inquiry form of the message. The RPG default handler sends it when the program had no MONITOR group, *PSSR subroutine or other handler for the error, and the job stops until someone replies. In a batch job the question usually goes to QSYSOPR. RNX0121 is the escape form with the same meaning. It doesn't wait for a reply and is what a MONITOR group or a calling program sees.

Common causes

• A %LOOKUP or LOOKUP that found nothing. %LOOKUP returns 0 in that case, and using the result directly as an index fails.
• A loop that runs one step too far, for example FOR i = 1 TO count when count is larger than the array.
• More data than the array was sized for, such as 60 lines loaded into an array declared with DIM(50).
• An index taken from the data, like a month number of 0 or 13, or a code that maps outside the table.
• An index variable that was never set and is still zero.

How to find the problem

1. Press F1 on the message. The help text names the array, the procedure, the program and the statement number. For a batch job, look in QSYSOPR (DSPMSG QSYSOPR) or the job log (DSPJOBLOG).
2. Find the statement in the compile listing and work out which expression is the index.
3. Reply D for a formatted dump, which shows the index variable's value when the program failed. Or rerun under STRDBG with a breakpoint on that statement.
4. Compare the index value with the array's DIM. A value of 0 usually points to a failed lookup or an unset counter. A value one above DIM points to a loop bound.

How to fix it

• Check the index before using it. It must be at least 1 and no more than %ELEM(array).
• Test the result of %LOOKUP for 0 before using it as an index.
• Use %ELEM instead of a hard-coded number in loop limits, so the loop follows the array if DIM changes.
• If the data really can exceed the array, raise DIM or stop loading when the array is full and report it.
• Reply C for the waiting job, then fix the program and rerun.

Technical reviewer: Albert Joseph, WND Software.

Last reviewed 2026-10-18 by the WND Software team. Written in our own words. For the full reference, check IBM’s documentation for your IBM i release.