Are there any other addons you have that might ?
Depending on how many addons you have active you could either load them one at a time to see if the error triggers to identify which addons might be the cause or you could do it in blocks until you narrow it down to a few and then repeat using the one at a time pattern.
Then its the case of testing that potential faulty addon to see if it repeatedly makes the addon happen when it is the only addon loaded, but not with no addons loaded. You can then pass the information on to the developer of the addon for them to look into.
However, unless an addon has literally recreated a PlayerName object it shouldn't have broken Blizzards one.
Lua Code:
function PlayerFrame_UpdatePlayerNameTextAnchor()
if PlayerFrame.unit == "vehicle" then
PlayerName:SetPoint("TOPLEFT", 96, -27);
else
PlayerName:SetPoint("TOPLEFT", 88, -27); <<<<< Error Reported on this line on Retail 10.1
end
end