FedEx's website lets you set a password of unlimited length (I've tested it up to 100), but when logging in, the password field has a maxlength of 25 characters, so it'll reject your >25 character password. If you override the maxlength in the HTML and enter the full password, then the form complains that the password field is empty.
@waldoj the same thing happens if you choose some special characters. That's how I got locked out, and while their tech support people are nice, they are *not* equipped to deal with this sort of thing.
The change happened pretty recently. Maybe someone upgraded some dependencies and it silently broke?