Acces to the gallery give you this error :

Fatal error: Call to undefined function: dom_xml__open_file()

This mean that your Web host don't support _xml_ dom.
The gallery is generated by the file gallery._xml_ (in components/com_flashitool/dessins/sandbox/) which contain the de_script_ion of drawings.

Perhaps you can inform admin of your Web hosting to activate _xml_ dom.

For the moment the component could not work on your web site.

I will try to fix it in futur release.