Hmm OK if the administrator at the time was using 10D media passwords and they upgraded without either removing the passwords before the upgrade OR deleting and recreating the jobs after the upgrade, then you will need to know what media password was in use at the time and add this into the properties of the catalog job when you go to run the catalog. If you do not know this password then you have a bit of a problem. So I guess the key question here is do you have that password? If you do not have the password, then you may need a specialist data recovery company to assist with extracting the data from the tape (which would be in MTF format)
If you are in this state then I would recommend immediately recreating any jobs that may have existed in 10D as these jobs will probably still be using media passwords even though you cannot see the configuration and can cause problems like this when it comes to a restore if your catalogs are missing (see below)
If you have edited jobs that came from 10D that had media passwords and added Encryption to them as well then you will need both the encryption key and the media password to catalog them and a Specialist Data Recovery Company will NOT be able to help because of the encryption.
If the catalog for the media still exists on the server, then even if a media password was accidentally in use you should still be able to restore, media passwords disable the ability to catalog the media.
Oh and if you do know the password then the Tech article already given involving BEMCLI is the way to use media passwords in 2012 and I am not sure why someone has given that post a negative mark.