Have you checked that the session var is being populated on the first page? Is the problem on that page rather than when the data is accessed on the next page? Try using this directly after you set the var:
echo '<pre>'; print_r($_SESSION); echo '</pre>';
Are you using session_start() at the top of all your pages?
Yes, I start session on page 2 and just this key in session array is empty. Maybe I put the problem too simple.
The long string comes from an iframe on page 1 generated by JS after inserting in image in wysiwyg editor. If you feel like looking into the problem to avoid potential future problem let me know, I'll post codes and describe the problem in detail.
As for now, I went round this problem inserting src attribute at a later stage and it works.
Thanks for your interest and help DC! Regards, Joey_33