Orokin Derelict - Can't Open Vault?

[Vindictus23]

I just recently heard about the vaults in Warframe (still pretty new to this game), and I made all of the keys and got an Orokin Derelict Extermination key thinking that'd be the easiest to solo and check it out before asking friends about it and seeing if they wanted to join. I just found the vault, and I know I have all 4 keys in my inventory. This vault requires the Decaying Dragon Key, which I know is made, but it won't let me open it. Am I missing something? I'd really appreciate an answer, thanks!

[(PSN)Crackle2012]

You have to equip the dragon keys and you can only equip one at a time, so it is better to run with a team and all four keys.

This /\ You don't just have to have them built.. you have to actually equip them in you "gear" in the "arsenal" and you can only equip one.  So 4 people with 1 of each key = 100% chance to open the vault

[Kinperor]

You need the key equipped in your "gear", otherwise you can't use it in a mission. 

[thececilmaster]

1.) You can only use a single key at any time.

2.) You must equip the key to your gear menu from the Arsenal. If you don't, you can't use it. That's where 1 comes into a bit more play.

[Frostosti]

you have to equip the key first from gear lijn arsenal menu

but you can only equip one key at a time

[[DE]Saske]

You have to equip the dragon keys and you can only equip one at a time, so it is better to run with a team and all four keys.

Edited August 25, 2014 by Saske92

[Vindictus23]

Well.. Major facepalm then. Thanks. c:

[Gillypud]

Just an addendum for the OP's benefit (since he says he's new). Each key comes with a debilitating factor when you have it equipped : -shield, -health, -speed and -damage. It's best to plan and use the keys that your frame/gear can overcome (bleeding key -health on rhino for example). Also, don't forget to remove the key from your arsenal once you're done with derelict.