If you want to get rid of an excess credit/deposit, enter a voucher to net it to 0 and then use AR-C and process a $0 payment to clear the aging

This is what I do for excess deposits in the Customer Deposit Screen
that I need to refund as a check or CC credit:
1. Use AR-C to put the deposit on account as an overpayment
2. Process a Customer Refund on that amount using AR-M
3. If it will be refunded as a check, print a real check from AR-M
4. If the refund will be a credit on their Credit Card, print a 'check' with AR-M using the DBA Checking account that the uncleared CC charges go to.
 
If it was just a mistake when the deposit was entered, you still need to do number 1 above, but instead of processing a customer refund, enter a AR Voucher like you would for a misc charge to the customer (freight, service charge, etc.) and then use AR-C to wash these out.
 
Now that I'm reading what I'm typing, if it was just a entry mistake in Customer Deposits, you could just enter an AR Voucher, then use AR-C to 'pay' the voucher with the deposit.

Maybe when you went to pay the voucher with the credit you entered the payment amount into AR-C.
 
To Apply a Credit to a Debit in AR-C, you specify a $0 payment.  It will want you to enter a check number ( I use 1 ), and also a Deposit Number ( I use 1 there too ).  Then in the payment screen, you select the Credit and Debit.  This results in a payment of $0.

you can actually just go in and delete a deposit.  no vouchers needed,  It just backs everything out.  If they actually overpaid then just do a refund check as mentioned before in prior post.