I purchased the software on Sunday, may 13th and am having the exact same issue. I have disabled the firewall on three different computers and get the same error message mentioned above:
Warning: mysql_pconnect() [
function.mysql-pconnect]: Access denied for user: 'mtu_download@198.170.88.131' (Using password: YES) in
/home/download/www/download.mtu.com/download.php on line
41
Unable to connect to database server!