>We are under VFP6SP5.. Is it kind object session here ?

that's the version i am working with. i have tryed that from the command window as well as from within a form. you can do this to create and set it:

oDS = CreateObject("session")
set datasession to oDS.datasessionid

* *** open tables
* *** ...code
* *** close tables

* *** to destroy the datasession:
release oDS

however, after reading your last post about the preview behavior, i think you will get the same behaviour with my solution.