Large-scale nmap scans - format and problems?

I'm having trouble with extremely large network scans and was wondering if anyone else was having issues. Trying to scan 16 Class Bs (yes, that's crazy but the company's IP schema is set up poorly) and it blows up all GUI versions of nmap but command line doesn't work much better. It can't seem to read from the list. I'm using 'nmap -iL - iplist.txt -PR -O -oX test.xml'

My goal is that it reads from the list, does a name resolution, OS identify, and outputs xml to a file. It seems to have major problems reading from the file AND when it errors out it prints my format back as 'nmap -O -oX -PR -test.xml iplist.txt'

Any thoughts or suggestions?

I've tried to replicate what you are doing but I only came across an issue when my IP list wasn't parsed properly; but that didn't give me the error you have. Have you tried using a list with just a handful of IP addresses to see if that works; and what version of nmap are you using?