Apparently, to fix this issue, we need to increase the Session state value.
I double-checked it by examining event logs and verified it. Event id: 7083 logged multiple times.
So, the fix is to increase the session state value. Here is how to do that:
Go to Central Administration >> Application Management >> Configure Info Path Form Services (under InfoPath Forms Services) and increase the value accordingly.
By default, it would be: 4096, in my case I increased it to: 8192, and the error gone away!
Another error in similar area:
users received errors in InfoPath forms, as – Number of form actions, 235, has exceeded 200, the maximum allowable value per request. This value is configurable and can be changed by the administrator.
And Event ID: 5737 logged multiple times. To fix this issue, increase the Number of actions per postback value