I have a problem with CKFinder for ASP.NET,please help!

I had just Integrated CKFinder into CKEditor.I edited the function CheckAuthentication() in config.ascx,just return "true" for testing, it works perfect at first.But when i check the authentication by a session validation(for example,check "Session["AdminName"] != null") I can't upload anymore.
Note:After I login I can browse the files on the server with the CKFinder,if i edit the CheckAuthentication() just return "true" I could upload files,if i check session validation,i could not upload.
Please tell me why ....Thanks for any reply!

My test environment:
VS2008,ASP.Net2.0