User session (HTTP/SMTP/..) closed after timeout

Hi Experts,

Web Dynpro ABAP application is getting called from Portal as soon as the user logged to the portal. i.e., As soon as the user logged to the portal, first iView which is displayed is Web Dynpro iView. But a strange error I can see is that at some times after login I get the following error.

Error when processing your request 
What has happened? 
The URL http://<hostname>:8000/sap/bc/webdynpro/sap/<appname>/ was not called due to an error.     
Note 
The following error text was processed in the system SID : User session (HTTP/SMTP/..) closed after timeout 
The error occurred on the application server hostname_SID_00 and in the work process 0 . 
The termination type was: ERROR_MESSAGE_STATE 
The ABAP call stack was: 
Method: PREPROCESS_REQUEST of program CL_WDR_CLIENT_ABSTRACT_HTTP===CP
Method: IF_HTTP_EXTENSION~HANDLE_REQUEST of program CL_WDR_MAIN_TASK==============CP
Method: EXECUTE_REQUEST_FROM_MEMORY of program CL_HTTP_SERVER================CP
Function: HTTP_DISPATCH_REQUEST of program SAPLHTTP_RUNTIME
Module: %_HTTP_START of program SAPMHTTP

This error in general comes when the user session expires after logged in and left the application idle for some time. But in my scenario this happens as soon as user logged into the portal. I found a notes 882548 ,1578632. But are not applicable in my case there is no parameter rdisp/plugin_auto_logout set in the profile.

Any suggestions to avoid this error.

Thanks

Murthy.