Sometimes I'll get the standard Blizzard error about disabling addons whenever I hit an action button on the default action bar. I haven't figured out what is the direct cause of it to reproduce it, but reloading the UI resolves the issue. I downloaded BugSack to see if I could catch what was going on and it returned this:

1x [ADDON_ACTION_FORBIDDEN] AddOn 'OmniBar' tried to call the protected function 'UseAction()'.
[string "@!BugGrabber/BugGrabber.lua"]:480: in function <!BugGrabber/BugGrabber.lua:480>
[string "=[C]"]: in function UseAction' [string "@FrameXML/SecureTemplates.lua"]:364: in function handler'
[string "@FrameXML/SecureTemplates.lua"]:690: in function <FrameXML/SecureTemplates.lua:672>
[string "@FrameXML/SecureTemplates.lua"]:704: in function <FrameXML/SecureTemplates.lua:697>
[string "@FrameXML/SecureTemplates.lua"]:746: in function SecureActionButton_OnClick' [string "@FrameXML/ActionButton.lua"]:109: in function TryUseActionButton'
[string "@FrameXML/ActionButton.lua"]:144: in function `ActionButtonDown'
[string "ACTIONBUTTON1"]:2: in function <[string "ACTIONBUTTON1"]:1>

Have a little more information on this one. Seems to happen everytime I launch the game. One /reload resolves it.