During the upgrade to 4.0, they broke the ad-packaging system. What you describe is exactly the same error I'm getting, and there is no fix. I think it is on the development roadmap, but seeing as this bug is essentially a major deal-breaker, I don't think this issue is getting enough attention. The whole ad-packaging system is completely useless.
Quick note: downgrading to SignageStudio 3.x will not work (I'm currently using 3.x myself). They broke the connection on their own end.