public static string ResolveFileName(string filename)
{
string fileName = null;
if (!Path.IsPathRooted(filename))
{
if (HttpContext.Current != null)
fileName = HttpContext.Current.Server.MapPath(filename);
if (fileName == null)
throw new InvalidOperationException("Could not resolve source filename.");
}
else
{
fileName = filename;
}
return fileName;
}