This is the number one reason.
Hence why I always add my portals by using the web interface, and in that way, I can just use cut&paste from the email I got, so guaranteed did not type an "l" (Lowercase letter L) instead of a "1" (number 1) or even an "I" (uppercase letter I) ; an "O" (uppercase letter O) instead of a "0" (number 0) or added any spaces accidently. Depending on google keyboard settings, it can sometime auto add spaces after a "." as you enter the URL. And I've seen bugs on some software (not saying buzz necessarily), where they don't trim the URL or user/pass and if you add a leading space or trailing space, it will cause an error also. And sometimes just a genuine typo of uppercase vs lowercase, or just the wrong letter. I have stared at passwords sometimes for so long convincing myself that they are "correctly" typed, yet there was 1 letter off
Best option if you have multiple boxes, why not just do a backup on the known working box, using the buzztv5 backup&restore option, and then restore it on the box that is acting up.