[Mediawiki-l] image resize fails

[WikiPlant]

hello.. when I try to make my images smaller, image magick doesn't work 
(unfortunately I can only enlarge pics) and there comes the warning that 
"shell_exec() has been disabled for security reasons in 
/www/htdocs/........../wiki/includes/Image.php on line 1037". the 
support of my hoster told me to create an .htaccess-file with 
"AddHandler php-fastcgi .php .php4 .php3", but then the wiki doesn't 
react anymore. please help me! the adress of my wiki is 
http://de.wikiplant.org/wiki/index.php/Hauptseite

greetings from berlin :) florian