you are getting this error because you're most likely are not using global variables.

one way to solve this is to disabled Display_errors in php.ini - CLICK HERE TO LEARN HOW

another way is to disable it in your php, CLICK HERE to disable error reporting

but the best way to do this is to make your script better.

if you have something like: if($_POST['foo']) or if($_REQUEST['foo']) change it to look like this:

if(isset($_POST['foo']))

so i just added the isset() function.