"Specified service does not exist as an installed service"

Ah, Windows. Such useful error messages. This one occurred after a teenager in my improv group asked for help with her Sansa Express 1 GB MP3 player -- a very nice item, BTW; I own an older Sansa myself, and the Express has everything I would expect.

Her ancién PC recognized the USB device, identifying it as an "MTP device." Unfortunately it declined to load an appropriate driver, instead pointing out the largely unintelligible error message above, and the flash storage on the MP3 player remained inaccessible (though the device would suck power for its internal rechargeable battery -- a very nice feature).

So, after searching around (notably here), I found nothing that worked; and, in desperation, rather than choose to have Windows find a driver for me, I told it I would specify a driver. Lo and behold, come time to choose what kind of driver to load, Windows gave me two choices only: MTP Device or USB Mass Storage. Hallelujah! I chose USB Mass Storage and, with very little further adieu, the new drive letters appeared in Explorer.

(The Sansa Express has internal flash storage and a removable Micro-SD slot, so one would expect two drive letters to appear. BTW Sandisk, now that I lust after this device, feel free to send one around! It's been out for nearly a year now, surely you can spare one. :P)