It looks like you hand coded that connection file and didn't use our webassist extension, so there is an error in it. I'd re-generate it with our extension, but the solution if you want to continue to use yours may be to just change mysql_error to mysqli_error on the line mentioned... but you could run into other issues down the line. The best bet is to use the webassist generated connection file instead of your own hand coded one.
The error you get is because the username and password is incorrect. Anytime you get "Authentication failed." it means that it is connecting to a database but the username and password aren't correct for getting data.