This is probably a somewhat common problem. When a mod that uses ace taints a frame for whatever reason (tainted means causes a popup to the effect of "Ace2 has been blocked from an action only availabl to the Blizzard UI"). Usually the name of the mod printed will be informative enough to track the problem down, but due to mods extensively using the Ace2 libraries it's difficult to track down specifically what's causing the problem.

My question is: is there any way to find out what addon is doing the tainting? Some ace mod has managed to taint my Raid window such that I can't promote people to various roles (raid assistant, main assist, main tank, master looter) and it is very annoying. It is always tainted, whether I am in combat or not in combat. I don't know what mod it is.

Any help or ideas would be greatly appreciated, on both my specific issue and the general issue of Ace2 frame tainting.

I have this issue also. The real problem is that the actual culprit is not always the one that gets reported by the blizzard error frame. Mine tells me that RDX is the tainting mod, but I really doubt that's the case.

Maybe you could list your mods and I'll compare against the list to narrow it down.

Dunno if it'll be any help but Skinner gave me some major taint issues until an update late yesterday. Similar issue, though it also tainted my spellbook in combat on top of that.

If you can duplicate the error message easly then all you have to do is, disable half your mods, replicate, if that fixes it disable the half of the addons still enabled if it doesn't then disable the other half, and repeat until you've worked out which is causing it.

Update ClearFont2

I have an even more fun version of the old "can't move people around in the raid while in combat" bug -- I can't even bring up my raid window or any of my social windows while in combat, nor my spellbook. I use a lot of fairly standard Ace mods and run WAU nightly. Has anyone known a particular 2.1 mod to cause this problem, before I start trial-and-error with all my mods?

As said earlier in this thread, Skinner was causing problems for most of ace2 users. I also heard about moveanything tainting issues.

There was similar thread in wowace forums, but not much info there =/

I know for a fact that AutoBar was causing huge issues until a recent update, though I'm sure you've gone and updated that one.

ItemRack is also the source of targetting problems people have been having, as well as other issues with frames in combat. Try disabling it if you're using it. Unfortunately, there hasn't been an update for it since 2.1 however.

I've heard of ClearFont2 being linked to some tainting issues as well, specifically not being able to move people while raiding.

I was having issues with not being able to move people while a fight was going on myself yesterday actually, which was quite annoying since it meant I couldn't switch in a new imp for our MT after one of our Warlocks had a brain fart at Shatter.

I don't use Skinner or MoveAnything. I don't get an "error" as such regarding illegal operations -- I just can't touch my raid window or spellbook (and also can't do things like a /who that'd return more than 3-4 results) while in combat.

Edit: I'll try disabling ClearFont first then and seeing if that helps. I definitely have been keeping it up to date, though.

Hrm post didn't go through for some reason.

Disable half your addons, if that doesn't fix it disable the other half, once you find which half is causing the error to go away then disable that half until you narrow it down to the addon thats causing it.

Yes I had this exact problem, I updated all my ace add ons a day or two ago and it fixed this problem. Don't know what was causing it though.
EDIT: To reproduce it, pretty sure you enter combat, then try open social or spell book frames, neither will open and the invisible frame will be there. Trying to open them again outside of combat fixes it.

I'm also having the issue whereby I cant promote people to Main Assist or Main Tank using the blizzard raid ui, causes seem to alternate between Prat and ClearFont2.

Yep this is basically a big part of the problem I have. I don't have ClearFont installed anymore, haven't in a while. I do have the fonts still installed into the font directory or whatever it is, but I doubt that's what is causing it. I use Prat so perhaps that may the link.

I'm almost positive that EnhancedQuestLog (or something like that) used to cause me to be unable to open my spellbook or raid frame in combat. If you have a quest log frame modifier, try disabling it.