Just solved the issue with the captcha not validating on the contact page.

I had a backup of the header.php file (without the captcha) in the contact us folder under pages. I named the backup 'header.php-bak.php' and it seems like Zen Cart was loading that file instead of the one with the captcha script! Renaming the backup file to 'backup-header.php.php' solved the issue. (Of course deleting or moving the backup file to another location fixes it as well.l)