BSP Error

Dear Friends,

In my BSP report there are two buttons and two text boxes

when i click preview buttons material details display in page according to entered materials with download button

when i click on the download button data refreshed in the earlier collected itab. therefore no data available for down load.

my coding flow is

Layout tab

<input type=submit name="onInputProcessing(PRVWE)"  value="Preview" style="height: 25px; width: 100px">

EventHandler

handle with case statement

    WHEN 'PRVWE'.

load data to itab

Layout tab

display itab data in the page with "download" button

<input type=submit name="onInputProcessing(DOWNLD)"  value="Download" style="height: 25px; width: 100px">

in this stage that loaded iteb data is missing itab blank no data come to display (file downloading_

am i missing some thing orr.....

any help please

Thanks in Advance