Why can I not delete a transfer transaction in my check register?

When I right click on the transaction, it only offers me to UNDO delete. I never deleted it because it shows in the check register. When I go to the account that it was transferred from, and try to delete that transfer to check register, it gives me the same message.
If I click on undo delete, it adjusts the balance of the accounts but then STILL does not allow me to delete the transfer. Thank you.