Hi Heather: When the invoice was Voided the system must have done something with the other side of the original payment entry. Which is why you are showing an amount in the Vendor's A/P account. (You said in your very first post that you had an amount in A/P and on the Vendor's Aged Report for A/P.) Make sure that the Vendor in question does have a balance showing. So in order to clear that amount and reverse the cheque through the bank account you should do the following:
1. Go to the Purchases Window, select the Vendor in question, and do an "invoice" to them that you enter the amount so that it credits Accounts Payable (which is what is automatically does) and instead of choosing an expense account to put the amount to, choose your Bank account number instead. This should debit back your Bank account and credit the Vendor's account to clear it.
2. BEFORE POSTING the entry, go up to Report (or Control+J) and see what the entry is doing. It should be making a Dr. to the Bank in order to cancel the cheque and a Cr. to Accounts Payable to clear the Vendor's account.
Have a look at this and let me know if it fixes the problem. Rita