A payment was made from checking to credit card ($152.06).
It matched a $152.06 payment to what was supposed to be a $4 reminder (incorrectly).
It matched it on the credit card side rather than checking side, I could tell because :
(1) I unlinked on the checking side, it failed, and also was not linked to a bank transaction:
(2) I then unlinked at the credit card side, and that was succesful …
I then had to DELETE the checking transaction that was created from the mis-matched transaction. This is the transaction which gave the above error.
Unfortunately, that did not put back my reminder which was mis-matched.
I will next have to edit the date of the next reminder for the $4 payment to fix that.
It's a mess, but i can work around this.