This error can occur if you're trying to delete a transaction that is linked to an inactive account. To successfully delete the transaction, you'll want to make the account active first.
- Click the Gear icon in the upper-right corner and select Chart of Accounts.
- Click the small gear icon (Settings) above the ACTION column.
- Put a check mark in the Include inactive box.
- Look for the inactive account (showing as Deleted) and click Make active.
Then, you can continue deleting the transaction.
Let me know if you need more help with this.