in the admin/common/properties.php file, change the following code:
$GLOBALS['permissions'] = array(
'dir' => 0777,
'file' => 0666
);
$GLOBALS['permissions'] = array(
'dir' => 0755,
'file' => 0755
);
then make sure that the permissions for the webassist/ckeditor/plugins/gallery folder, and all files underneath it are set to 755