framework service under sub application httpcontext.session is not work

We have various framework web from sub application in the same website. I just started trying to use adapter to migrate one application, but it couldn't get Session["key"] without any error message. Reference #175 , build the the same sub application name (virtual path) between Core Website and Framework Website, it still couldn't get Session["key"] anymore. But when I put the framework application to the root, it work fine.It Seems framework application must in the root website? or shouId I make other setting to get Sessions for sub application?