First, do a Verify on the media that is being used when you get this message. This can take 3-4 hours for LTO-4 media. This will read the tape from start to finish, when done, update the tape header and update the Internal Database
If this does not help, you may want to make sure that you have the latest Cell Server and Media Agent patches installed. I seem to recall that there have been some kind of fix involving a simiiar error