1. Create a new pledge gift with the same information, and set up the installment schedule with the proper frequency, # of installments, etc.
2. Apply payments from the old pledge to the new pledge.
3. Delete the pledge that is causing the error message/scheduling problems.

OR

Write off the existing pledge and create a new pledge for the remaining balance with the appropriate schedule.

OR

Change the amount of the original pledge to reflect the amount paid to the existing pledge, and create a new gift for the remaining balance with the desired schedule.