The library's mechanism for determining the type of media in a slot or EE port failed. This is usually the barcode reader or some other sensor that is part of the robotics.
The volume is skipped by the process.
Determine the reason the library could not determine the media type, such as deteriorated barcode, scanner failure, or other hardware problem as determined by system engineer. If the barcode label is replaced on a private volume containing data, it must be with a label having the volume name. Scratch volumes or empty private volumes can be replaced with any barcode but they must be re-labeled if the barcode name changes.