AsyncFileUpload Control ?

Question

I have a page that contain One AsyncFileUpload control and another one is Button control. I want when i click on button means Button Click Event Call then File Save in Folder(Here name is Currency).My code at Button Click event  is:

string m_file = AsyncFileUpload1.PostedFile.FileName;

AsyncFileUpload1.SaveAs(Server.MapPath("Currency/" + m_file));


But File not save at target folder? What's Problem ?