Not getting fb session in begning android

Not getting fb session in begning android

I am working on Facebook SDK. I have done many things such as download
photos, uploading photos, creating new albums and many more and all are
working fine.
But now I have a problem in getting FB session. Actually I have three
activities for ex. A, B & C.
In B activity user login successfully and in return he get an session. And
I can get this session in C activity and A activity also. But only in
following sequence. B to A, B to C, B to A to C, B to C to A. no matter I
close the application or not.
But when I close the application and open activity A I am not able to get
the active session. I also try this in facebook sample project
"SessionLoginSample". But similler things happens. I also try to save
accessToken and get this session but It doesn't work.
Actually I am try to create an library for future use.