You'd have to let us know what exactly the content of
fuBanner.FileName
is.
Is it a fully specified file path to an image on your disk?
Is it may be a relative URL?
In the former case you'd have to check what
System.IO.Path.GetFullPath(fuBanner.FileName)
returns.
In the latter case you'd need to find out the file's path in the filesystem:
mappedPath = HttpContext.Current.Server.MapPath(fuBanner.FileName);
Regards,
— Manfred