asp.net Exception: The Local Security Authority cannot be contacted

I have two applications (A)anonymous authentication and (B) windows authentication (A) called Handler from (B)

when I use the following code exception ( The Local Security Authority cannot be contacted) be displayed

code:

WebClient webClient = new WebClient();

webClient.Credentials = new NetworkCredential(UserName, password, domain name);

string url =(handler url) 

webClient.DownloadFile(url,Context.Server.MapPath(imagePath));