I'm playing Classic wow and am receiving the following error:

Date: 2019-11-06 22:34:39
ID: 1
Error occured in: AddOn: HideBlizzard
Count: 1
Message: Note: AddOn HideBlizzard attempted to call a protected function (TargetFrameToT:Show()) during combat lockdown.
Debug:
[C]: Show()
..\FrameXML\TargetFrame.lua:910: TargetofTarget_Update()
..\FrameXML\TargetFrame.lua:109: TargetFrame_Update()
..\FrameXML\TargetFrame.lua:150:
..\FrameXML\TargetFrame.lua:142
[C]: CameraOrSelectOrMoveStop()
[string "CAMERAORSELECTORMOVE"]:4:
[string "CAMERAORSELECTORMOVE"]:1

Were you trying to toggle "Target Unit Frame" option while in combat?

It's complaining about a tainted function that it hasn't accessed yet. I believe this is a blizzard bug.