I am having the same problem as the person above.
It is not clear that you have to enter this id and it doesn't give indicators as to how to do this. I have now registered to Feedburner and have an id and have tried 3 times!
I have entered the little tail code at the end, the whole code and the code with the /com.
That's three out of three possibilities, right? Please can you provide detailed instructions if there are others or do I need to go to a particular Feed burner site that works with WP? Please provide this if so.
The current details assuming that users have the same knowledge as you about IT ... but I don't.