Howdy SenTineLs,
Thank you for the feedback regarding the issue that Leonardo and yourself are having. So you are saying that the issue is occurring on the 4.2.1 build of UE4 but not on the 4.3 build correct, or is the issue still occurring in the most recent build?
I would highly recommend that you, if possible, use an updated version of the engine so the issue will no longer occur. There have been multiple build failed issues over the last couple of UE4 releases that have addressed the packaging section.
Thanks and have a great day!