Error "Session Timed Out" When saving webi report as PDF

Hi,

I am getting below error when saving  report as PDF

The Session Timed Out.The document *.wid has been auto saved  in the Favorites~WebIntelligence Folder..Click Restore to retrieve it.

(ERROR : WIJ600001).

I get above error in PROD  but works fine in DEV.

Version :  BOE 3.1 SP7 (DEV & PROD).

Session Time out  set as  one hour.

Report runs for 3 minutes .once I get the data if I try to save it as PDF immediately I get the above mentioned Error.