Ok, thats a little more helpful
What you are getting is a (off the top of my head) Show.MessageBox(Ex blah) which, to you pops up on your desktop, it looks like a small window (gray box) with the text 'NCN Index out of range' or something? and a 'Ok' button in the center? If I am incorrect, tell me.
I believe the error isn't caused 100% by the NCN class, but maybe the data type used to store the information? Datatype being 'int64'
Like I may have mentioned before, I am not 100% savvy with dougies work, within the project you should have either/both connections.cs and/or players.cs? Within both/either of those files, you should find the data types saved for EACH player! Look at what 'Int64' data types you have and let me know, I am not sure how I or anyone else can help, but I will try, I am sure others will too.
Someone who is using dougies work, help me out here!
NPL = Someone joins the race from spectate
NCN = Someone connects to the host (also happens when you start the application)