At the end of the installation, the script asked for a new password for the DB in the line:
mysql -peLaStIx.2oo7 -e "SET PASSWORD FOR 'root'@'localhost' = PASSWORD(' ')"
if you remember that password go to /etc/freepbx.conf and correct the password in the value:
$amp_conf['AMPDBPASS'] = ''
the file comes with a default and I guess it shouldn´t be changed.