The only issue I can reproduce is if you leave any of the project ID, version, author or description fields empty, these get left empty in package.appxmanifest and cause VS2015 to say the file is invalid. In the next beta C2 now prompts for these to be filled in if exporting for Windows 10 which should prevent this happening. I believe all other issues are either just having the wrong components of VS2015 installed, or are otherwise unrelated, so please file separate issues for those if you still have trouble and are certain you have VS2015 installed correctly and have filled out the project ID, version, author and description fields.