Found the solution
Thanks for your suggestions. I figured out a soultion. Incidently I changed the player name and after that it was not detected on the same computer. The soultion is connect the player to a computer, then go to "Device Manager" find out the entry for Creative Zen player (under "Portable Media Player"), right click on it and select "Uninstall". Then disconnect the USB cable from the computer and reconnect it, and windows will install the new device ("New" since you had uninstalled it) and it works fine. This may be applicable to other players as well.