Had the same problem and nearly went nuts trying to fix it. Here's what I did:
1. Uninstall all creative driver & creative software.
2. Uninstalled Windows Media Player 11 (Rolled back to WMP 10) and restarted PC.
3. Uninstalled Windows Media Player 11 Runtime and restarted PC.
4. Downloaded and Installed the latest free version of Winamp from http://www.winamp.com
5. Connected my A/C Power Cord to my Nomad Jukebox then connected my Nomad Jukebox via USB cable to the Computer.
The computer should then recognize the Nomad Jukebox as "Found New Hardware" then "MTP Device" and lastly "Your new hardware is installed and ready to use.
6. If you haven't already, go to the creative website and download the Creative Zen Xtra PlaysForSure Firmware 2.10.03 and save it to your computer.
7. Run the Firmware (Make sure Nomad Jukebox is connected) and at this point the Computer should recognize the Nomad Jukebox and begin the upgrade.
After your upgrade is complete, You can go ahead and re-download Windows Media Player 11 and it will recognize the Nomad Jukebox.Not sure what version of windows you have, but I have two computers, one with windows xp and the other has windows 7 and Im able to transfer music perfectly fine with Windows Media Player and RealPlayer on both computers. I hope this works for you. Good Luck!