That error code means there is a problem in the PHP file that iis “listening”, not the grid in this case. At the top of the php file enable error reporting like this:
<?php
error_reporting(E_ALL);
ini_set('display_errors', '1');
?>
Then retry the edit and this time you should see some other useful info as to what the problem is.
Could be something as simple as a missing “;” at the end of a line.
