Could not upload files to Mapped network drives.

Hi All,
        I have created an application to upload files to a mapped network drive(say: Z:\), but is showing the error:
System.IO.DirectoryNotFoundException: Could not find a part of the path 'Z:\****\********'.
What i did:
Created a web page with FileUpload control & a button.In button click event i have used the code as below.     


if (FileUpload1.HasFile)
{
FileUpload1.SaveAs(ConfigurationManager.AppSettings["FileUploadPath"].ToString() + FileUpload1.FileName); ...