Oracle Message ORA-19551 - device is busy, device type: string, device name: string

ERRORdevice is busy, device type: string, device name: string
CAUSEThe indicated device could not be allocated because it is allocated to another session, or no device was named, or all devices of the requested type are busy.
ACTIONEither attempt to allocate another device or wait until the required device is no longer busy.