Actually, it was my unfold of the helmet. I wasn't aware that there were any other unfolds.
Also, to be honest, I didn't have many problems with this pep. There are just a lot of small pieces.
Just wanted to say thank you for the file. I've spent the past 5 hours going through the Official Reach pepakura thread to get here but now I can finally begin building my first halo build. Thanks again!