I just returned to WoW and was told that many people moved from Bagnon to this one. This is the first time ever I'm reporting bugs but I've been getting so many it is interfering with their new UI. Here iare the error(s) I received:

1x [ADDON_ACTION_BLOCKED] AddOn 'LiteBag' tried to call the protected function 'ActionButton1:SetAttribute()'.
[string "@!BugGrabber/BugGrabber.lua"]:481: in function <!BugGrabber/BugGrabber.lua:481>
[string "=[C]"]: in function SetAttribute' [string "@FrameXML/ActionButton.lua"]:485: in function UpdatePressAndHoldAction'
[string "@FrameXML/ActionButton.lua"]:551: in function Update' [string "@FrameXML/ActionButton.lua"]:503: in function UpdateAction'
[string "@FrameXML/ActionButton.lua"]:980: in function `OnEvent'
[string "@FrameXML/ActionButton.lua"]:207: in function <FrameXML/ActionButton.lua:204>

Locals:
_ = Frame {
RegisterEvent = defined @!BugGrabber/BugGrabber.lua:487
0 =
UnregisterEvent = defined @!BugGrabber/BugGrabber.lua:487
SetScript = defined @!BugGrabber/BugGrabber.lua:487
}
event = "ADDON_ACTION_BLOCKED"
events =

{
ADDON_ACTION_BLOCKED = defined @!BugGrabber/BugGrabber.lua:553
ADDON_ACTION_FORBIDDEN = defined @!BugGrabber/BugGrabber.lua:553
PLAYER_LOGIN = defined @!BugGrabber/BugGrabber.lua:547
LUA_WARNING = defined @!BugGrabber/BugGrabber.lua:562
ADDON_LOADED = defined @!BugGrabber/BugGrabber.lua:507
}

3x [ADDON_ACTION_BLOCKED] AddOn 'LiteBag' tried to call the protected function 'PrimaryProfession2SpellButtonBottom:Show()'.
[string "@!BugGrabber/BugGrabber.lua"]:481: in function <!BugGrabber/BugGrabber.lua:481>
[string "=[C]"]: in function Show' [string "@FrameXML/SpellBookFrame.lua"]:1557: in function FormatProfession'
[string "@FrameXML/SpellBookFrame.lua"]:1600: in function `SpellBook_UpdateProfTab'
[string "@FrameXML/SpellBookFrame.lua"]:163: in function <FrameXML/SpellBookFrame.lua:142>

Locals:
_ = Frame {
RegisterEvent = defined @!BugGrabber/BugGrabber.lua:487
0 =
UnregisterEvent = defined @!BugGrabber/BugGrabber.lua:487
SetScript = defined @!BugGrabber/BugGrabber.lua:487
}
event = "ADDON_ACTION_BLOCKED"
events =

{
ADDON_ACTION_BLOCKED = defined @!BugGrabber/BugGrabber.lua:553
ADDON_ACTION_FORBIDDEN = defined @!BugGrabber/BugGrabber.lua:553
PLAYER_LOGIN = defined @!BugGrabber/BugGrabber.lua:547
LUA_WARNING = defined @!BugGrabber/BugGrabber.lua:562
ADDON_LOADED = defined @!BugGrabber/BugGrabber.lua:507
}

1x [ADDON_ACTION_BLOCKED] AddOn 'LiteBag' tried to call the protected function 'MultiBarBottomLeftButton1:SetShown()'.
[string "@!BugGrabber/BugGrabber.lua"]:481: in function <!BugGrabber/BugGrabber.lua:481>
[string "=[C]"]: in function SetShown' [string "@FrameXML/ActionBar.lua"]:196: in function UpdateShownButtons'
[string "@FrameXML/ActionButton.lua"]:507: in function <FrameXML/ActionButton.lua:492>
[string "=[C]"]: in function UpdateAction' [string "@FrameXML/ActionButton.lua"]:980: in function OnEvent'
[string "@FrameXML/ActionButton.lua"]:207: in function <FrameXML/ActionButton.lua:204>

Locals:
_ = Frame {
RegisterEvent = defined @!BugGrabber/BugGrabber.lua:487
0 =
UnregisterEvent = defined @!BugGrabber/BugGrabber.lua:487
SetScript = defined @!BugGrabber/BugGrabber.lua:487
}
event = "ADDON_ACTION_BLOCKED"
events =

{
ADDON_ACTION_BLOCKED = defined @!BugGrabber/BugGrabber.lua:553
ADDON_ACTION_FORBIDDEN = defined @!BugGrabber/BugGrabber.lua:553
PLAYER_LOGIN = defined @!BugGrabber/BugGrabber.lua:547
LUA_WARNING = defined @!BugGrabber/BugGrabber.lua:562
ADDON_LOADED = defined @!BugGrabber/BugGrabber.lua:507
}

1x [ADDON_ACTION_BLOCKED] AddOn 'LiteBag' tried to call the protected function 'MultiBar7Button1:SetShown()'.
[string "@!BugGrabber/BugGrabber.lua"]:481: in function <!BugGrabber/BugGrabber.lua:481>
[string "=[C]"]: in function SetShown' [string "@FrameXML/ActionBar.lua"]:196: in function UpdateShownButtons'
[string "@FrameXML/ActionButton.lua"]:507: in function <FrameXML/ActionButton.lua:492>
[string "=[C]"]: in function UpdateAction' [string "@FrameXML/ActionButton.lua"]:980: in function OnEvent'
[string "@FrameXML/ActionButton.lua"]:207: in function <FrameXML/ActionButton.lua:204>

Locals:
_ = Frame {
RegisterEvent = defined @!BugGrabber/BugGrabber.lua:487
0 =
UnregisterEvent = defined @!BugGrabber/BugGrabber.lua:487
SetScript = defined @!BugGrabber/BugGrabber.lua:487
}
event = "ADDON_ACTION_BLOCKED"
events =

{
ADDON_ACTION_BLOCKED = defined @!BugGrabber/BugGrabber.lua:553
ADDON_ACTION_FORBIDDEN = defined @!BugGrabber/BugGrabber.lua:553
PLAYER_LOGIN = defined @!BugGrabber/BugGrabber.lua:547
LUA_WARNING = defined @!BugGrabber/BugGrabber.lua:562
ADDON_LOADED = defined @!BugGrabber/BugGrabber.lua:507
}

This is what Blizzard calls "taint", addons interfering with the default UI elements and causing them to stop working (mostly) in combat.

Unfortunately what addon is responsible isn't correctly reported by the error messages. I'm 99% sure LiteBag isn't the cause, as I haven't had any taint issues in many many months and nobody else has reported any.

I don't think there's any good way to track it down except for disabling addons and trying to see which one caused it. If you get a taint error with only LiteBag loaded and no other addons please report it here #34.