i had the same problem recently and found out it was because the file was just over the size limit (which for me on my server is 2.0M). try splitting your file into a couple of smaller files or increasing the limit on your server in the php.ini file (i hear that helps but i just split mine into two and it worked).
I’d like to see the ability to organize pages by parent.
Thanks for this info. It’s on line 215 in my version. Works like a charm. I prefer not wasting extra time building a custom menu when page order already works, if I don’t have to. Just another thing to fuss with, IMO.