Think I am going mad here..
So I have a working website setup in IIS. This was all configured by a previous developer. We have a set of reports that you can browse to by going to localhost/Reports/ReportName, the underlying directory structure in IIS is actually Reports/Views/ReportName/index.cshtml. I have added a new report with the exact same setup as the others however when I navigate to the localhost/Reports/NewReportName URL I get a 404 and I am not quite sure what I am missing...