I believe Gemini is not compatible with Orbiter 2016
I've learned that hard way ?
but like a 72-75 said... you should have write which Orbiter version you use.
if it's some older version then Gemini should work for you
Project Gemini 2.0 can work in O2016 since most of it is coded in Spacecraft and MS2015. That being said, this requires editing all scenarios one by one to be fully compatible