I am trying to launch the default application registered for an extension specifying an additional argument:
ProcessStartInfo p = new ProcessStartInfo();
what exactly is your "argument", does it have spaces, backslash, etc?
Process process = new Process();
process.StartInfo.FileName = @"C:\process.exe";
process.StartInfo.Arguments = @"-r -d something else";
process.StartInfo.CreateNoWindow = false;
process.StartInfo.UseShellExecute = false;
process.Start();
Is there any reason why you cant start the app, then use the extension and arguments in your arguments?