Any good references for streaming in a large XML file?

I have a pretty large XML file (around 600Mb) that I need to stream in and pick out certain elements to act on. I’ve noticed that with the code I have currently, it seems to work great on smaller files, but when I hit a certain amount of records, it appears to miss quite a few elements that it should hit on.

I’m guessing I have a flaw in my logic somewhere, but I’m not that well versed in handling XML. Based on that, I need to brush up and I’m looking for some decent references centered around streaming.