Hi Prasad ,
Are you selecting an entry in a DDLB or in a F4 help pop-up . ?
In the case of the F4 help pop-up , you can always code in the on close event you have defined for the pop-up .
In the case of DDLB entry selection see the thread Event after select a value in Dropdown List Box (DDLB)
Regards,
Vineet