Roland GR-640 User Manual page 124

then double-click it. The name of your machine or
Unknown device appears below the selected item.
Click the name to select it.
From the Action menu, click Uninstall.
On the Confirm Device Uninstall window, select the
Delete the driver software for this device check
box, and then click OK. Close Device Manager.
The name of your machine or Unknown device appears below the selected
item. Click the name to select it.
Disconnect the USB cable from the computer, and
then restart Windows.
Follow the procedure in "Uninstalling the Driver
(Windows 7)" and uninstall the driver.
Follow the procedure in "Installing the Driver for
Windows" and reinstall the driver from the
beginning.
http://startup.rolanddg.com/