1. Click the Schedule button on the gift record
2. Click Reschedule
3. Enter the date of the next due payment in the Reschedule installments dues after field
4. Enter the same frequency as was on the original schedule - except for the number of installments, enter the number of remaining unpaid installments
5. Enter the date of the original next due payment in the 'Starting on' field
6. Click Next, then Finish, then OK
7. Click File, Save on the gift to save these changes
8. Select Gifts, Adjust. You should now be able to adjust the gift without error.