exception in runtime file creation

See more:

ASP.NET

C#5.0

Exception:

The UNC path should be of the form \\server\share.

i am creating a log file for maintaining a log and error. but its showing a exception.

string dir = HttpRuntime.AppDomainAppVirtualPath + "\\Log Files";

             if (!System.IO.Directory.Exists(dir))
             {
                 System.IO.Directory.CreateDirectory(dir);

             }


             string logFile = dir + "\\ErrorLog.txt";

it is firing exception after line System.IO.Directory.CreateDirectory(dir);
this exception is shown after deployig website is it releted to deplyment?

plz help.