If you're getting the message that Blizzard blocked blah blah--then you have a tainted addon.
I'm currently having the same problem with sixUI and Subspec addon; it's not easy to fix--have to figure out what the addon is doing to taint the button function.
Just to add: I have same problem with trying to queue for battlegrounds, clicking on spells in my spellbook, and some collection toys will trigger it as well.
If you enable taint logging you will probably see something very close to this;
Code:
11/8 20:33:33.476 Interface\FrameXML\SpellBookFrame.lua:1009 SpellBook_GetSpellBookSlot()
11/8 20:33:33.476 An action was blocked because of taint from SixUI - CastSpell()
11/8 20:33:33.476 Interface\FrameXML\SpellBookFrame.lua:560 SpellButton_OnClick()
11/8 20:33:33.476 SpellButton2:OnClick()