A typical error is as follows:
Warning: mysql_errno(): supplied argument is not a valid MySQL-Link resource in /path/to/forum/inc/db_mysql.php on line 313 MySQL error: Warning: mysql_error(): supplied argument is not a valid MySQL-Link resource in /path/to/forum/inc/db_mysql.php on line 314
This means MyBB cannot connect to the database. The database connection settings are either incorrect, or the MySQL server is down.
- Make sure that inc/config.php exists, and the database connection settings are correct.
- Contact your webhost if the MySQL server is down (ie. if you try to login to phpMyAdmin and get the same error, then most likely the MySQL server is down).