Extract the BigBuffs addon to your UI/Nightfall directory.
Open eq2ui_mainhud_target.xml in Notepad.
About the 3rd line down you should find
Code:
UserMovable="true">
Replace with
Code:
UserMovable="true" Version="2.0">
Do the same with eq2ui_mainhud_impliedtarget.xml.
Not possitive but I don't think anything else changed since that addon was posted.