Expected refund after amendment, received payment notice

I amended my tax return because a capital loss carryover was missed.  The amended filing showed an expected refund.  Instead, weeks later, IRS issued a payment due notice.

 

The transcript shows: 290 additional tax assessed

 

Called IRS and they said "Qualified Dividend Capital Gain Worksheet was used when Schedule D should have been used".  This could be a red herring so take it with a grain of salt.

 

What could be going on here?  How should I proceed?