Once done with the reef, you can't go back (no destination), and it's not missions, just the two cuts from the two times you have to go there from Venus.

That was a bit confusing to read. Can you further explain what happened?

Just unlocked Venus My friend said Hey want too play the 1st mission! I said yeah He was already almost done with it We beat it The he said hey I got the reef So we started watching the reef cutscenes I had too go I left in the middle of the cutscene False alarm,so I came back online I was gonna play the reef mission The planet was there but no mission I've played all the Venus levels now and watched the second reef cutscene but still I can't play the mission I left destiny in my xbox for a few days So that may be the problem So when I got off today I quit destiny and took out the disc Im planning on playing later too see if anything has changed

You might wanna try having your friend start the mission with him again and see if it will let you play. Get back to me about it and tell me what happens before I actually pit it as a listed bug.