I would have to agree. I removed Doublewide and my errors have gone. So has the kick ass quest log..
This happens right after a fight with a quest mob. Hope this info helps.
12/8 10:01:45.061 Execution tainted by DoubleWide while reading QuestLogTitle23 - getglobal()
12/8 10:01:45.061 Interface\FrameXML\QuestLogFrame.lua:139
12/8 10:01:45.061 QuestLog_Update()
12/8 10:01:45.061 Interface\FrameXML\QuestLogFrame.lua:66 QuestLog_OnEvent()
12/8 10:01:45.061 QuestLogFrame:OnEvent()
12/8 10:01:45.061 An action was blocked in combat because of taint from DoubleWide - MultiBarRight:SetPoint()
12/8 10:01:45.061 Interface\FrameXML\UIParent.lua:2287
12/8 10:01:45.061 securecall()
12/8 10:01:45.061 Interface\FrameXML\UIParent.lua:2342
12/8 10:01:45.061 UIParent_ManageFramePositions()
12/8 10:01:45.061 Interface\FrameXML\QuestLogFrame.lua:688
12/8 10:01:45.061 QuestWatch_Update()
12/8 10:01:45.061 Interface\FrameXML\QuestLogFrame.lua:67 QuestLog_OnEvent()
12/8 10:01:45.061 QuestLogFrame:OnEvent()
To shorten my post here is a clip of the rest of the errors. They all have the same body, st the first line is what changes.
12/8 10:01:45.061 An action was blocked in combat because of taint from DoubleWide - MultiBarBottomLeft:SetPoint()
12/8 10:01:45.062 An action was blocked in combat because of taint from DoubleWide - PossessBarFrame:SetPoint()
12/8 10:01:46.297 An action was blocked in combat because of taint from DoubleWide - MultiBarRight:SetPoint()
12/8 10:01:46.297 An action was blocked in combat because of taint from DoubleWide - MultiBarBottomLeft:SetPoint()
12/8 10:01:46.297 An action was blocked in combat because of taint from DoubleWide - PossessBarFrame:SetPoint()
12/8 10:01:46.305 An action was blocked in combat because of taint from DoubleWide - MultiBarRight:SetPoint()
12/8 10:01:46.305 An action was blocked in combat because of taint from DoubleWide - MultiBarBottomLeft:SetPoint()
12/8 10:01:46.305 An action was blocked in combat because of taint from DoubleWide - PossessBarFrame:SetPoint()