ok will be fixed in next version, the downloader.http plugin is now partly overriding the "upload" action, adding the subMenu dynamically, thus only if active (nice demonstration of the XML framework flexibility :-) )
Clearing the server cache Delete the two files data/cache/plugins_*.ser
Clearing the client cache Delete your browser navigation data (cache, cookies, etc).
It's a PHP config A configuration that AjaXplorer cannot update directly, but that is set in the php.ini file. Some configs must be changed directly inside this file, other can be overriden by an .htaccess file inside the AjaXplorer folder.