What is a Blocked mission?

I've got some missions in a special Blocked section in my quests list. I can't start them at all.

What are Blocked missions? Can I complete a Blocked mission if I join a game where the Host can complete the mission? Will it count as completed for me too?

Solution 1:

Since I have fairly low progress through the main plotline, I'm not sure of all causes of "Blocked" missions. One cause that other players like this one have experienced is some type of lock that occurs once you near the final mission.

Note that all missions become unblocked after you complete the game, so you're not locked out forever, you can just complete the story. Missions are generally blocked for plot-related reasons.

Solution 2:

Blocked missions are missions that you currently cannot complete, usually because of story related events.

Spoilers:

for example sanctuary taking off in one of the main missions blocks all the side missions you have that have to be delivered to an npc in sanctuary.

As to your second question yes you can finish that quest in another persons game and it would count for your character aswell.