Yeah looks like it's not loading at all.
In your shoes I would do this:
/script DEFAULT_CHAT_FRAME:AddMessage(tostring(TipReaderTooltip))
and if it says nil, then the xml isn't loading at all. I'd check the .toc to make sure you named it ok and there are no spaces at the end of the filename(s). Then I'd check the FrameXML log in the Logs folder or load it up in Firefox to look for errors. That's if you don't use an XML-validation program (which you may given all the extra stuff in the <Ui> tag.)
It also helps to simplify the XML to find out where it's croaking:
Code:
<Ui>
<Script file="ToolTipScan.lua"/>
<GameTooltip name="TipReaderTooltip" inherits="GameTooltipTemplate"/>
</Ui>
See if DEFAULT_CHAT_FRAME:AddMessage(tostring(TipReaderTooltip)) returns a table or nil. If a table, then the mod loads and the element is seen. Can add stuff now:
Code:
<Ui>
<Script file="ToolTipScan.lua"/>
<GameTooltip name="TipReaderTooltip" inherits="GameTooltipTemplate">
<Scripts>
<OnLoad>
this:SetOwner(WorldFrame, "ANCHOR_NONE")
</OnLoad>
</Scripts>
</GameTooltip>
</Ui>