Hi Hazem,
What do you mean by "a new session is opened"? Do you get a blank screen or the first screen of the Shopping Cart creation transaction?
In the first case check SAP note 1511147 for Internet Explorer security settings, in the second case I would check if the data sent from the catalog are all valid. For this check the previous thread:
http://scn.sap.com/thread/3335567
Regards,
Timea