Do you mean to say that if you research Shamans as your first thing, that blocks you from Tier 4 research?
I think Nuju just meant that you have to have researched Shamans before you would be able to research Charm. You would have to have researched some of the unit types, though, so that couldn't be the problem for the entire master category.
EDIT: You need to research something on the Expert level to get access to the Master level.
... of course I already have Shamans researched. I'm 19 turns into the game. I am saying that I can literally research NOTHING on that tier, despite having the prerequisites and money.
Nope, Raze, I'm pretty sure this is bugged. I do have things researched on the Expert Tier. I have the Devastator, but can't pick up "On the Double". I can't research the Juggernaut or Bomber Balloon.
Aha! I think the problem is because I loaded a saved game. I saved and continued a campaign game last night. Just before going to sleep, I manually saved, then researched Imp Fighters, and quit the game without saving again.
Loading the game I saved last night, now I cannot research anything at all on the Expert Tier, even though I bought things from it previously. That's probably also why I cannot research the master tier stuff: I tried to do that after loading a previous saved game.
EDIT: No wait, now the research menu seems to have fixed itself - both tiers. I'm not sure why. It is a fresh turn now, though.
