I cannot log in as a specific user, while the password i put in is correct.
As root you can login, can't you? Else you actually have kind of a problem - tricky, but solvable.
Could be a code page problem. I guess, that's what
SirDice meant with "Maybe hitting a language barrier".
Example to explain:
german and english KBs have switched Z and Y keys. If your computer is set to an english code table while you generate your pw, and if your password was 'noisy', you type 'noisy', but the computer saves your pw as 'noisz'.
Then when you login as an user with a german code page, and you don't respect the keys switched, you again type 'noisy', and this time your computer gets 'noisy', but expects 'noisz', so wrong pw.
You may try passwords using keys only matching english KBs and your local ones (I do that for my root password for when my machine does not come up far enough to provide my local code page.)
But that's only temporary, because for both cases - setting a pw, and login - the same code table shall be active, and used, which is the case within a default installation by the FreeBSD installer.
You have to dig for that either to get a clean solution, what got wrong - if code page was the actual cause for that, which you can also test by trying pws having english and local key codes matching. (In fact just the same keys need to be pressed - what's written on them the computer does not know; it simply receives a code from the KB which key was pressed, not which letter is assigned to it. That's job of the OS with code pages.)