In some PHP environment, you will see "Notice: Undefined index" error messages shown, along with the actual plugin. This is due to the over zealous error reporting setup for PHP environment by default.

To hides these messages, open your php file (such as easypaypal.php for Easy Paypal), add the following lines after the first occurrence of
"<?php":

//------------------------------------------------
// Turn off all error reporting
error_reporting(0);
//------------------------------------------------

This should get rid off all these warning messages.