I have a windows service which is using a method from a class library with same asp.net solution. in class library, I have a method with following line:
re
It could be that when you are using windows service, you are no longer running a web app, therefore HttpContext and web server is not available. Try using System.IO.File for mapping, see whether that takes you to the correct directory.
Edit
private String yourFullPath = System.IO.Path.GetFullPath("/YourDirectory") + @"\";