What do you mean by "401K amt"? Are you talking about a 401(k) contribution amount that was deducted from your pay (shown with code D in box 12 of your W-2)? Or are you talking about a distribution from a 401(k) account that was reported on a Form 1099-R?
Where exactly was the 401(k) amount omitted from? It would help if you give specific form and line numbers that the 401(k) amount was omitted from, where you think it should have been included.
Keep in mind that the calculation of the credit for income tax paid to another jurisdiction is based on only "Income actually taxed by both New Jersey and the other jurisdiction." "Income must be taxed by both New Jersey and the other jurisdiction to be included on Schedule NJ-COJ." You might find New Jersey Publication GIT-3W helpful in understanding the details of how the calculation is done. The preceding quotations are from that publication. You can download it from the following link.
GIT-3W Credit for Income Taxes Paid to Other Jurisdictions (Wage Income)
