Please try restarting the device. This will clear the Google cache and (hopefully) fix the error.
On the Forward Cloud Menu, there's a checkbox for enabling and disabling devices. Use it to remove devices from your registered account. In the desktop version, you can use the little computer icon to the top left of the screen. Hovering over the icon will indicate its functionality.
On the Forward Cloud Menu, make sure the option "Device is enabled" is turned on. In the desktop version, make sure you click the little computer icon (last icon in the top-left row of icons) to enable/disable your device.
Tap the cloud icon to open the account options screen. Enter a new password in the 'password' and 'repeat password' fields. Tap Save. If the problem persists, write to us at firstname.lastname@example.org