In my register is a transaction that I already manually entered, and in the category is a transfer to another account. The bank sends a transaction, same date and amount, a completely different payee, and no category. My entry and the bank's do not automatically match (they never did). I used to drag/drop to match, but now that just gets rejected with no feedback, so I use the menu and get the unhelpful error that is the title of this post. They still won't match even if I modify the bank's transaction to have the same payee and transfer. This used to work in the past, so I suspect it is an improvement.