I've spent the last few days battling this issue. I've finally sussed out our specific problem and thought it worthwhile sharing. The error was the same as the original posters with iTunes Connect giving a "There was an error importing this build." error as follows:
I tried all sorts to solve this but in my travels the give away of the problem was that one of our many *.bundle files was appearing in the 'Binary and Entitlments' list during the upload/submission process:
Digging a little further when I inspected the contents of that particular *.bundle (with-in either the *.ipa or in the build folder of derived data) there was an unexpected unix executable file. None of other *.bundle files contained a unix executable.
After some trial and error I was able to prevent the executable from being created and added to the bundle by changing the "VERSION_SYSTEM" build setting to "None" (it had inadvertently been set to "Apple Generic" in some recent xcconfig changes).
Anyway, that solved the problem for us. Hope it helps.
An alternative (but less desirable) solution was to remove the (empty) "Compile Sources" step from the targets "Build Phases".
