The problem is on the PC with Windows 7 and WiMP12. (Media Player 12 is standard with Win 7).
You can fix the MTP connection as follows:
Turn on the Clip and go to Settings > System Settings > USB Mode and manually select MTP. This will hold the device in MTP mode.
Plug in your device, and open the Device Manager. Click on the Sansa under Portable Device and select Properties, then select uninstall while connected. I know this sounds counterintuitive, but what you are doing by this operation is telling the PC to clear the registry entry for the recognized device.
Unplug the Sansa, and wait about 30 seconds for the operation to complete (or to be sure, restart the PC, but you shouldn’t have to with Windows 7).
Now plug in the Sansa once again, in a few seconds, it will show “connected” on its display, and you will then see a popup stating “new device found, MTP Device”. This should do the trick. Once the PC registers the device, MTP should now work.
The biggest advantage to using MTP is that playlists can be built using Windows Explorer (via a right click on your music), or with Windows Media Player, and playlists are possible using both the internal and external memory, as pla format playlists.
The downside of the MSC / MTP communications difference with the Clip or Clip Zip is that the USB controller in the Sansa onlyworks with one mode at a time,so music transferred in one mode is “invisible” to the PC while in the other mode, so you need to have all of your music transferred in one mode. The Fuze+ has a different controller that allows both transfers to be accessed simultaneously.
I’m having a similar problem; I use Rhapsody and the program won’t recongnize my Clip as a MTP device, and therefore won’t let me transfer subscription music to it. I’ve had no trouble with this Clip on a previous Win7 machine and a Vista machine before that. I’ve tried your solution, but when I reconnect the Clip in MTP mode, the PC says it can’t find the driver. If I connect it in MSC mode, the PC will find the driver and install it, but then can’t see it as an MTP device.