I am having the same issue as B-MUSIC-school. I cannot delete any A/R accounts, even though they all have $0 balance. They each have 2-10 transactions in them from almost 20 years ago. However, none of the transactions are linked to inactive accounts. They are also not any of the 3 types of accounts you mention (Accounts used by a product or service, Income accounts that have un-invoiced charges, or Accounts that QuickBooks needs). They are plain and simple A/R accounts. And I get this error message: "This account cannot be inactivated because there are transactions in it that have a non-zero balance."

Is the ONLY solution to go through and delete all of the transactions within the accounts? That seems insane and bad practice. Why are A/R accounts seemingly impossible to delete?