CHECK APPSERVER LOGS. THE SITE BOOTED WITH INTERNAL DEFAULT SETTINGS, BECAUSE OF: bea.jolt.ServiceException: Invalid Session

This comes generally due to the application server is down.

1) Try to boot the application server by deleting the cache and then login again to PIA.

2) If still it gives the same error. Then try to IPC resources with psadmin.exe utility. It's the 10 option over there as shown below.

psadmin.exe

3) Still if it's showing the application server is down then reboot the application, webserver by deleting the cache and up it. Check the application server logs for detail of the error if any.