This is pretty much the "report bug" section of site, most bugs are errors and can be sorted out and the best place to post is right here.
First thing I say since the last patch is make sure you run SVN update and SVN revert. Also make sure you don't run update.lua, some people use an autoloader for the bot and have update included in that batch file.
If after that it's all green then next is to look at the error.
In your case it is getting an error when it is trying to update the target and returning a nil value.
Which means that something has gone wrong along the way as it should have a target if you just killed it.
Try the SVN update and SVN revert and see if it helps, if not then post again with more details please =)
Remember no matter you do in life to always have a little fun while you are at it