After keeping the system idle , system is not prompting for re-login but gives a internal server err

Hi All,
When the instance is kept idle for some time and when we try to navigate to other responsibilities after keeping the system idle for some time.
The instance is asking for re-login, when i click on Yes , normally it should prompt for username and password but in our case its giving us Internal Server Error Page.

Please help as this is happening in production instance.
Screen shot enclosed.

With Regards
Uday Raju