Try this procedure.
Disconnect the PB from the computer.
Uninstall the Device Manager.
Reboot your computer (for good measure)
Connect the PB using the USB cable.
Now you should see a PlayBook CD-ROM.
In that CD-ROM you will find version 7 of the Device Manager, install it.
Once installed disconnect the PB from the computer.
Wait for about 20 seconds then plug it back in.
Windows should detect new device and start Device Manager. It may take up to two minutes for windows to detect and properly install.
Then device manager will map 'z' drive to the PB.
