why it is showing your session is timeout using stateserver session mode..

I have a website. it have 3 subsite...

I am using stateserver session mode for 2 subsites (site1 and site 2) and I am using same machinekey for both sites

But is it working for site1... and it is not working for site2...

i can able to login... and i can access the some of the pages,

but it prompting "your session has been time out" for some of the pages

help me resolve this issue.