FF can flash AOSP ROMs. I recommend that my users use it as an alternative to SS. Try going into SuperSU and changing it from prompt to grant on the FlashFire entry, then try again.
Excited to see you at work! You used a 5.0.1 I noticed, why not use a 5.0.2 build from the international section?
Thanks for the tip mate, I'll try that later soon i get off work