What is the error message "The used command is not allowed with this MySQL version" indicating in PHP scripts after upgrading to MySQL 5.5?

The error message "The used command is not allowed with this MySQL version" indicates that the MySQL query being used in the PHP script is not supported by the upgraded MySQL version 5.5. To solve this issue, you need to update the query to use commands that are compatible with MySQL 5.5.

// Example of updating a query to be compatible with MySQL 5.5
$query = "SELECT * FROM table_name";
// Update the query to use a supported command for MySQL 5.5
$query = "SELECT column1, column2 FROM table_name";