Dumb question: did you "using System;" at the top of your .CS file?

Yes, I was using System.

There seemed to be a problem with System.Random and UnityEngine.Random. Fixed it now by specifying everywhere I used a 'Random' function which library to use.

Thank you all for the help.

Oh, if you're in Unity, I suggest just using their random, instead of mixing and using System.Random as well. At least until you decide that you need a better random than either and roll your own =)