Placing Towers on Path help

So I started working on the solution while looking through previous discussions on the challenge. I found one particularly helpful solution which was built very similarly to mine and used it as a troubleshooter for most of my work. However, on attempting to compile so that I could run I got the following error:

error CS1061: Type `TreehouseDefense.OnPathException' does not contain a definition for `message' and no extension method `message' of type `TreehouseDefense.OnPathException' could be found. Are you missing an assembly reference?

I'm nost sure how to handle this error and would like some help. I'm still very new to C#.

I've included code snippets of what I wrote:

Firstly I wrote the code that would check for the tower location and throw an exception, should the tower be on the path.

Then I went over to the Exception.cs file and wrote the exception handler.

Thirdly I went over to the Path.cs file and wrote the OnPath method. This was based on another students' solution. I was pretty much lost on this step.

And, finally, I went to Game.cs, added the exception handler and attempted to create a tower on the path to test it.