Message: Usage: local volume = C_VoiceChat.GetMemberVolume(playerLocation)
Time: Fri Aug 3 18:37:47 2018
Count: 1
Stack: Usage: local volume = C_VoiceChat.GetMemberVolume(playerLocation)
[C]: in function accessor' Interface\FrameXML\UnitPopupCustomControls.lua:8: in function CallAccessor'
Interface\SharedXML\PropertySlider.lua:13: in function UpdateVisibleState' Interface\FrameXML\UnitPopupCustomControls.lua:47: in function OnSetOwningButton'
Interface\FrameXML\UIDropDownMenuTemplates.lua:21: in function SetOwningButton' Interface\FrameXML\UIDropDownMenu.lua:669: in function UIDropDownMenu_CheckAddCustomFrame'
Interface\FrameXML\UIDropDownMenu.lua:649: in function UIDropDownMenu_AddButton' Interface\FrameXML\UnitPopup.lua:754: in function UnitPopup_AddDropDownButton'
Interface\FrameXML\UnitPopup.lua:543: in function <Interface\FrameXML\UnitPopup.lua:285>
[C]: in function UnitPopup_ShowMenu' Interface\FrameXML\SecureTemplates.lua:237: in function initFunction'
Interface\FrameXML\UIDropDownMenu.lua:77: in function UIDropDownMenu_Initialize' Interface\FrameXML\UIDropDownMenu.lua:1085: in function ToggleDropDownMenu'
Interface\FrameXML\UIDropDownMenu.lua:203: in function <Interface\FrameXML\UIDropDownMenu.lua:198>

Locals: (*temporary) = "Usage: local volume = C_VoiceChat.GetMemberVolume(playerLocation)"

I do not know in what extent this has to do with the databar ...
I don't see anything concerning the addon in the error stack you pasted