Hi,
Please check the following SAP note:
1059623 - Re-logon required when launching BEx Web App from BEx Tools
Please do look at this SAP note 1059623 completely.
Also, please look at the following SAP note:
701205 - Single Sign-On using SAP Logon Tickets.
For further information on the same please take a look at the following:
Single Sign-on using SAP Logon tickets
http://help.sap.com/saphelp_ep50sp6/helpdata/en/89/6eb8e1af2f11d5993700508b6b8b11/frameset.htm
Thanks & Regards,
Sapna