Believe it or not I've had this issue appear with Aurora, well the lua error blamed Aurora. I looked in the toc just now and guess what? Several XML files are called for in it.
Code:
FrameXML\AlertFrames.lua
FrameXML\FlexRaidFrame.lua
FrameXML\Fonts.lua
FrameXML\LFDFrame.lua
FrameXML\LFGFrame.lua
FrameXML\LootHistory.lua
FrameXML\ModelPreviewFrame.lua
FrameXML\ProductChoiceFrame.lua
FrameXML\PVEFrame.lua
FrameXML\QueueStatusFrame.lua
FrameXML\RaidFinder.lua
FrameXML\RecruitAFriendFrame.lua
FrameXML\RolePoll.lua
FrameXML\ScenarioFinder.lua
FrameXML\SpellBookFrame.lua
FrameXML\StaticPopup.lua
FrameXML\TaxiFrame.lua
FrameXML\WorldStateFrame.lua
I may just try removing them and see what happens and if the error repeats.
Edit* - Aurora does need these in the toc or it doesn't skin the frame mentioned.