Blizzard changed the way the API works to make it impossible for an addon to dispell buffs whilst in combat.

This has been rectified, however, and it's now only impossible for addons to automatically dispell buffs - but you should still be able to click them off.

It's likely that some of your addons haven't been updated to take these changes into account - even though it often seems like the most random thing preventing you from doing things, that seemingly has nothing to do with the function you're trying to perform.

Until your addons are updated to reflect the changes, I'd recommend macro'ing the /cancelaura function to your action bar - then you can dispel whatever you need whenever you want to.

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Well it's nice to get some info, however these addons have been updated since this issue started so maybe the author isn't aware there is an issue.

And I already said I do NOT have any addons that disable buffs for me or even touch that part of the UI visually, it's the default Blizzard buff UI.

I also said at first I am allowed to dispell buffs with a certain addon enabled but at random while I'm playing the client suddenly says that Auctioneer is stopping me from dispelling buffs...Why does it freak out midgame, why not at the start?

I think I heard that Nbuff has the ability to click off buffs (look at this week's Reader UI article - they talk about it). I know I used to use SBF for my buffs, and it was really frustrating to have to type /cancelaura for everything. I know my rogue was ESPECIALLY annoyed during the Thanksgiving-themed one where everyone was turning me into a turkey (ugh).

Are you running a UI addon such as Xperl? An addon that changes your portrait frames can prevent debuff cancelation due to a change on blizzards end (from what I understand). Ive been dealing with the problem due to xperl, though there may be a change for it out and I just havent looked. I've just been typing or macroing /cancelaura [spell name]. Hope that helps.

This happens to me all the time too. I'll be fine for the first while after I log on, but eventually it will stop letting me click off buffs. It'll be annoying when I'm trying to parachute onto something and miss since I can't cancel the slow fall buff. The addon that's the trouble for me is ouf, which handles the unit frames for Spartan UI. The main thing that bugs me is that, like I said, it'll work fine for a while, but then suddenly decide it doesn't like me being able to cancel the buffs and stop working. Why is it not one way or the other?

My UI is almost 100% Default, unit frames, actionbars and Buffs (Minimap and bags are the only things changed but they've never been 'Blamed' by the client, only Auctioneer, Mats Battle Text and a few others which barely change my UI at all)

I've seen some discussion by Addon authors about this. It seems this is a Blizzard problem, as it will sometimes blame addons that have nothing to do with the UI. The fact that it's random (as to when or how often it happens, and which UI it blames) adds weight to the argument that this isn't and addon issue per-se.

I'm just going by what they say, but these are some authors that I put a lot of faith in.

Btw, there are other actions that "addons" supposedly prevent you from performing as well. Just thought I'd mention that.