This is related to the 'NT8 Strategy design essentials' course I just purchased.

The first step in the course is to find the Ninjatrader.Custom.csproj  file and I did. It can be opened as an individual file in Visual Studio but it cannot be opened as a project/solution, I keep getting the error window mentioned below: 'The selected file cannot be opened as a solution or project...'

Any ideas what can be happening here?  I've been using NT8 for a few months now but I just accessed VS for the first time yesterday.