Hi Vinod,
Please check sap note below mention
1757252 - How to analyse problems related to session loss or logoff in CRM WebUI
Symptom
Randomly the users in CRM get disconnected from their WebUI session and loose all their current data. It is not reproducible and difficult to analyze. Also the symptoms vary:
Session timed out
Logon prompt popup for username and password
Auto logout from CRM Webclient
Regards,
Vaibhav Shah