You can run MA missions if you are invited to the team but you are not allowed to create missions using the Mission Architect or to start missions from the MA terminals.
From Avatea's Trial Account Restrictions post:
Players using Trial Accounts are subject to the following restrictions:
They can be invited to teams that are using the Mission Architect Missions but they will not be able to access Mission Architect terminals to create, rate or start any published Mission Architect Missions;
They cannot level past level 13;
They may earn Influence/Infamy but only up to 50 000;
They may be invited into a team but cannot join Super-Groups;
They may communicate with other players but cannot email other players and may only speak in the Local (/local), Help (/hc) or Team (/team) channels.
Trial Accounts will have those restrictions active until they are upgraded with either:
an online serial code purchased from the online NCsoft store,
an NCsoft Game Card (purchased from a participating retailer) or
a serial code from a City of Heroes / Villains boxed retail product.
EDIT: Added link to post and contents.
If the game spit out 20 dollar bills people would complain that they weren't sequentially numbered. If they were sequentially numbered people would complain that they weren't random enough.
Black Pebble is my new hero.
Can people who are on a free trial use the MA? Cause when I tried, I was told I couldn't access MA from there.