Paragon Mission?

i can change my sub but paragon isn't one of them.. D: You haven't given much info, so I'll assume the worst.

1) Do you own Nightfall?
2) Is Nightfall linked to your account?
3) Is the character trying to change secondary to the Command Post yet?
4) Have you completed the quest "Building the Base: Prisoners of War"?

All of those things must be done to change a secondary to Paragon (in addition to the 500 gold fee). If you are trying to change secondary in Factions or Prophecies, you can't. If you are trying to change secondary at the Great Temple of Balthazar, you can only do so once 'ascended'. No matter where you change, you have to own Nightfall and have it linked to your account.

If its a PvP character, it simply needs to be on an account with Nightfall active, and all you do is press 'K' and select the secandary you want.

If you are trying to change secondary in Factions or Prophecies, you can't. If you are trying to change secondary at the Great Temple of Balthazar, you can only do so once 'ascended'. No matter where you change, you have to own Nightfall and have it linked to your account. A couple things here. First, while you cannot change to paragon in prophecies as the secondary profession changers are profession specific, you CAN change to a paragon in factions if you have NF on your account and you are ascended/closer to the stars.

And as a note if it is a non-NF character, just getting to the command post and doing the building the base is not enough, you will still need to ascend, otherwise the profession changer will tell you to before he talks business with you. Thus, getting ascended is required at ANY prof changer. You probably only notice this in GToB because in Cantha, by the time you get to Senji's Corner, you are guranteed to have ascended, and in Elona, for Elonian born toons, you have "ascended" before you can go anywhere near the profession changer.