[App_rpt-users] USB Devices keep disappearing off device list on DELL SFF PC's

Hi All; Has anyone experienced an issue with the USB fob and other devices that keep on falling off the device list on DELL SFF PC's? This is happening on 2 separate DELL boxes (I don't have the model # handy).. one box is an Asterisk / app_rpt box and the other is a D STAR box communicating with an external GMSK modem. Thx! Ramesh.