验证问题是一个已知的问题与PHP 5.3及以上版本的MySQL。检查：

http://www.bitshop.com/Blogs/tabid/95/EntryId/67/PHP-mysqlnd-cannot-connect-to-MySQL-4-1-using-old-authentication.aspx

If I open up a cmd shell and run

>mysql --host=12.34.56.78 --port=1234 --user=myuser --password=mypassword mydb

I can successfully connect to the remote mysql database.

But if I create a php page on my localhost containing

<?php
$hostname = "12.34.56.78:1234";
$username = "myuser";
$password = "mypassword";
$dbname   = "mydb";
$connect = mysql_connect($hostname,$username,$password) or die ("Error: could not connect to database");
?>

I get the following error:

Error: could not connect to database

Can anyone explain what might be causing the problem here?

mysql_error() => mysqlnd cannot connect to MySQL 4.1+ using old authentication

Auth problems are a known issue with PHP 5.3 and older versions of MySQL. Check this:

http://www.bitshop.com/Blogs/tabid/95/EntryId/67/PHP-mysqlnd-cannot-connect-to-MySQL-4-1-using-old-authentication.aspx