IRS Form MO-CR wants me to "describe nature" on line 4 and won't let me file without it. What does it want entered?

[BillM223]

The instructions on the form (see here) are :

"Lines 3 & 4 - Enter the total amount of wages, commissions, and other income you or your spouse received from the other state(s) or District of Columbia, as reported on the other state(s) return."

Since line 3 is "wages and commission", they apparently want other income types on Line 4.