Vendor payment entry through deposit slip

Hi

I have this strange transaction. User created deposit slip entry to vendor account by using AR payment journal.

Transaction goes like this

1. I am recording a payment we received from a customer.

2. Then I go to the “Add Lines” to the Journal batch I just created and select “New”, making certain that the deposit slip is selected.  Then go to the “General” tab.  Under the Account selection, change the Accout type to “Vendor” and select a vendor account number.  Change your offset account type to “Bank” and select your bank account.  Enter the amount of the cheque

3. Validate and post

Now user want to reverse this entry. if I use 'Cancel Payment' option from Deposit slips, it gives me error -"Unable to find customer transaction for reversal. Verify that a customer offset transaction exits for the deposit slip." This error is obvious because user posted transaction to vendor by using AR deposit slip.

 So.. how to reverse or cancel this particular transaction..

Thanks

Girish