It's the Star Alliance Airline Award inventory management system.
Please see the article linked below as to why United's blocking of flights in the system is contriversial:
Originally Posted by
DogHead
"We manage award availability on our Star Alliance partners just as we do with United's own saver awards," said Jeff Kovick, a United spokesman ... "It is an ongoing balance of ensuring we meet our customers' interest in award travel on partner carriers with United's need to generate revenue on our own flights."
So there you have it... from the horse's mouth.
Full story here:
http://washingtontimes.com/news/2008...award-tickets/
As StarNet is used by all members of the Star Alliance, I'd ask any follow-up questions regarding it be asked in the Star Alliance Forum. There are also a number of existing threads in this forum that deal with United's policy of blocking award availability on partner airlines, should you wish to obtain additional information on that topic.
Thank you,
FlyinHawaiian, Co-Moderator
United Mileage Plus Forum