Well, that's because the nice folks at proseries don't consider a not-for-profit to be a business.  Put another way, their sales pitch is misleading, they know it is misleading, and they basically think you should have noticed that Form 990 wasn't included on the list of return-types that you can use the 15 business returns for.  Nevermind that the accounting world thinks of From 990 as a business return, or that Form 990 is included in the "business software download" as defined by proseries itself.