goto your cpanel
goto the folder where you installed the media wiki
goto extensions
create a new file called wikiscript.php
http://www.mediawiki.org/wiki/Extension:WikiScript#Source_code
add the source code from the link above BUT (this is very imp) leave out the ?>
with the ?> the page gives an error WebResponse.php on line 16
http://www.mwusers.com/forums/showthread.php?11744-mysterious-bug-WebResponse.php-16
find the file LocalSettings.php and add the lines below
#Added for allowing user javascript
require_once( "$IP/extensions/wikiscript.php" );
DONE!!!