I use Quickbooks 2017 desktop, and while running a routine backup, the file verify operation generated an "Error 196" and suggested that I re-enter online banking information for a certain credit card account. It's not clear why this was a problem, as I had no issues going online to download transactions on a regular basis.
I was unexcited about fully disconnecting and reconnecting the account from my bank, but after going into the Bank Feed Setting it showed a curious error:
Odd: everything works, but it's somehow unhappy with it (and MyUsername is how I login to my bank).
Looking at the other account with the same bank, the same screen showed myusername - in all lower case - so on a hunch I went to the failing account and changed it from MyUsername to myusername.
Poof: that fixed it. How about that.
And as a curious aside, for some time I had wanted to rename the account to reflect the last four digits of my updated account number (say, from 1234 to 9876) just so it's easy to correlate with account activity, but Quickbooks would just freeze when I tried to edit the name, but after this username fix that started working too.