That app isn't necessary. You just plug in the phone to your desktop/laptop with the microUSB and it automatically mount itself as a separate drive. If it doesnt, go into the settings, and change the option.
1. Plug the phone into USB port.
2. Windows will notify you that your device has been found and is ready for use.
3. On the Droid pull down the Notifications bar and touch the "USB Connected" notification.
4. A pop up window will appear. Select "Mount".
5. Your Droid is now available in Windows File Explorer as a "Removable Drive"