I was just building help files/references for AdDuplex Windows Phone Silverlight control and XNA library using the awesome Sandcastle Help File Builder. Silverlight portion went pretty smoothly. Just had to add references to a couple of phone specific assemblies. But with XNA I immediately got this error when trying to compile:
Error BE0067: Unable to obtain assembly name from project file '[projectFile]' using Configuration 'Release', Platform 'Any CPU'
Problem is that in XNA project the Platform is not “Any CPU” but “Windows Phone” (in my case). OK, but there’s no such option in SHFB list:

And there’s no way to expand that list with your own values.
Fortunately you can specify Configuration and Platform as properties for each documentation source separately in a free form text:

Problem solved. Hopefully this helps someone.