I am Integrating pay pal to my site and using Pay pal PDT.
i AM USING HTML BUTTON OF PAY PAL AND i AM SETTING SEESION[uSERNAME"] IN my pay pal button page. from there it goes to pay pal and returns back to my thank you page.
On my thank you page I am reading this session.
Sometimes its there and sometimes it null.
Some times Session expires after returning from pay pal to My site after payment.
P-lease let me know the reason if you can guess