Well, I think i've managed to solve the reCAPTCHA problem on my 5.4.1 version ...
Here's what I did:
I've changed the "include/recaptchalib.php" with this one: (that is the official recaptchalib.php delivered by the guys from
recaptcha.net )
recaptchalib.php
After that I went to
recaptcha.net , i signed up and i got from them the
public and private keys for my site.
Then, in "Tracker settings/Security settings", I choose Recaptcha, entered the keys (public and private), and saved the configuration ....
And that's it!
To me works perfectly !!!!