First step: Please confirm your keyboard settings.
It happened once to me, from one version to the other the naming
convention for Latinamerica Spanish keyboard settings had changed from
"LA" to "LATAM" - and unknowingly (unsuccesffully) is was trying to
log in using a "Laos" keyboard setting. It took me a couple of weeks
to find that out and solve it changing the conf file in terminal mode.

Disregard if your username looks ok and your password does not contain
any strange character.