The error message is pretty useful. It tells you in which file to look (civ4leaderheadinfos.xml), at what line the error is (19) and exactly what the problem is (the parser is expecting iEspionageWeight, but the tag is iRefusetoTalkWarThreshold).
I suspect that you originally made your mod for vanilla civ or warlords. There are some additional tags that you have to include before it works with BTS.
I actually made a little script that can do that for you:
script. If you can't run it (you're not running Linux I suppose

), you can still have a look at it to see where the differences are. The last ten lines are relevant for civ4leaderheadinfos.xml. A short example:
Code:
if line.find("<iWarmongerRespect>") != -1:
line = ConvertUnits().InsertData(line,"<iEspionageWeight>0</iEspionageWeight>")
This bit of code simply tells the program (or you in this case) that a tag iEspionageWeight should be added after iWarmongerRespect. This will get pretty boring after a while (especially for units), so I recommend using a BTS unit/building/whatever as starting point for new mods, not vanilla/warlord ones.