I am trying to add a reference 'Newtonsoft.Json.dll' I have followed what he has asked. which adds this ref from 'browse' tab to 'recent' tab. If I look at the list of refs from the ref list it is listed but with a yellow flag.
When I hold the cursor over the flag it says: not available as it does not exist, or is not built?? So I have removed it from the list of ref's and try to re-add it.
It only appears in the 'recent' section and when I add it, I get:
A reference to 'Newtonsoft.Json.dll' could not be added.
Its probably something in your build system: the dll is likely getting cleaned (as in deleted by a rebuild), or is in a directory that isn't under your solution, or simply isn't getting copied to the output directory.
I'm sorry I don't have a more specific piece of advice. What I'm going to do though is suggest you use a shot-gun to kill a mosquito: use NuGet. In C# with Visual Studio (or any other .net IDE), you really want to use the nuget package manager, since it works so well.
This will put it in a library directory, include it in the build path, and allow you to use the Intelli sense to auto-add the appropriate reference from your project.