how to stop workitem complete or how to keep work item in inbox based on conditions even if it completed

Hi,

my requirement is to call webdyn pro screen from workflow..

i am calling webdynpro screen by using FM :CALL_BROWSER from workflow.

when webdyn pro screen is called user will enter some values . if user closed webdyn pro screen with out entering any values we need show this workitem in his inbox. so that user can again open it and enter values in the webdyn pro screen.

Please help how to stop work item complete based on conditions.

Thanks,

phani