Our Report Studio users are getting a "DPR-ERR-2079 Firewall Security Rejection. Your request was rejected by the security firewall." error in report studio after a period of inactivity. This is a new distributed installation of C10 and we didn't receive this error in C8.4. Users could leave report studio open for hours with out any errors.
What have you set in 'Inactivity timeout in seconds' field in cognos configuration under authentication?
Give it a big value such as 28800 and see if that works.