Just commenting on this for now: can you change the version to a specific (existing) firmware? 5.0-4418 is the version I've been using, since it's 5.0 beta (first version to work with DSM5.0 toolchain). 

I already corrected it in both the mono and nzbdrone packages that I have ready, so alternatively, I could push it if you want me to (means you need to rebase your fork though)