Unable to take mission in group, 2 players, UIT and Serco nations.

Error giving mission: You cannot have this mission.

Player levels:
5/7/5/9/4
15/15/14/18/17

I've seen this too

Generally because it's one nation sanctioned. What are the faction standings?

Were you in a group?

This is basically the worst error message possible...

Unable to take mission in group, 2 players, UIT and Serco nations.

Yes, he was in a group..