Lost Shell Extension

I've grown used to using the shell extension i.e "right Click"/MP3Tag to open folders. It just disappeared today, granted it's a new installation of Win 7 x64 but the extension was there, but then disappeared. I guess I can just reinstall the program but I'd like to know why it went away and how to get it back w/o re-installation. Thanks

You can check with http://www.nirsoft.net/utils/shexview.html if it is still there and if it is disabled.