A previous bookkeeper created invoices to account for cash sales. Then when the deposits were made they were not properly applied to the invoices but were created new. Therefore there is a balance in the A/R that should not be there.

Sounds like the sales was duplicated, once when the invoice was made and once when the deposit was made. (That's really only one entry to begin with. I'm glad it's a previous bookkeeper.) If that is the case, then do a credit in the A/R account and charge it to the sales, which will be a debit and reserve out the duplicate.

If the sales wasn't recorded twice, then you'd have to debit whatever account was used.

This is all assuming I'm interpreting you correctly.