2161251 - Error "User is missing credentials for connecting to alias ... " throw out for WebFlowConnector

End user log on to portal and access uwl, there is warning An error occurred while trying to connect to the provider displayed. After clicking hyperlink Click for details next to warning, there is message like User is missing credentails for connecting to alias <System alias>. Contact your system administrator. displayed. See below image as an example. And this warning only happen to few end user. For system administrative user like j2ee_admin/admin, no such warning is displayed.

"Image/data in this KBA is from SAP internal systems, sample data, or demo systems. Any resemblance to real data is purely coincidental."

• SAP Universal Worklist (UWL)
• SAP Enterprise Portal 
• SAP NetWeaver
• SAP Composition Environment

User is missing credentials for connecting to alias, An error occurred while trying to connect to the provider, click for details, display connection status, WebFlowConnector, Exception occured, uwl, universal worklist, com.sap.portal.connectivity.ConnectivityRuntimeException , KBA , EP-BC-UWL , Universal Worklist , BC-JAS-SEC , Security, User Management , BC-JAS-ADM-ADM , Administration , Problem