so maybe that is the reason why the tape initially became poor. Maybe due to polling or RSM the header became overwritten when the DP backup still was acive. So if after a scan the media still is blank, this means the header information is not available and without media header the import becomes impossible. But the behaviour was not initated by DP. Anyway and sorry, it seems you will not be able to restore data from this specific media anymore.
Any kind of IO error will mark the tape as Poor. Generally speaking, it can be set back to Good using 'omnimm -reset_poor_medium' command
However, as Daniel said, some IO errors are more extreme than others. The way that you describe your symptoms lead me to think that the last time this tape was used, you probably got 2 errors
If you see these errors, chances are that, while writing to the tape, the drive got a rewind signal, which corrupted the Header file. This would not be known until the tape rewinds, and checks the Header file, and finds it to be corrupt
The most common cause for this is having a service enabled 'Removable Storage Manager' (RSM). This does not have to be turned on on the immediate Media Agent. If you are in a SAN, it can be running on any system that has access to the Tape Drive / LIbrary, and that system does not have to be in the Data Protector Cell. The SAN administrator would have to identify what systems are zoned to see the tape library
I had a guy once that found that, in his case, his laptop was zoned to see the tape library, and was causing these errors
Check all systems that are zoned to see the Tape Library, if you find the RSM service running, stop it and disable it from starting automatically
I agree with Daniel, nothing is recoverable from this media