Borderlands help

[LandR]

I just beat the last boss in the vault and got a final mission to do. It's called turn in vault key to tannis.

The problem is I can't turn it in. I walk up to Tannis, click square. It comes up with the mission to turn it in as normal but it doesn't let me turn it in ?

I can't complete the game, what do I do ?

[LandR]

Well, apparently it helps if you actually pick up the key after beating the boss...