In Windows 7 my Device stage icon would always appear when i plugged in my Sansa Fuze, now it doesnt appear for any of my Device Stage-compatible devices, even though they are set to launch it.
So the problem is with Windows. Try support.microsoft.com .
this happened to me once before and i was able to fix it by uninstalling the device in device manager and then rebooting the computer. then i reconnected my clip+ and device stage was working again like normal. hope it helps.
You might want to check if your Sansa Fuze is on MTP mode(Settings > System Settings > USB mode > MTP). I believe Device Stage will only pop up if it is on MTP mode but im not possitive.