showModalDialog Problem in PostBack in ASP

Question

I would like to have a lookup form in my ASP app. So I use client script to popup a Lookup aspx page and the page will display a grid and let use to select. and the code to pop the form is listed below retval = window.showModalDialog( "ALookup.aspx", window); But I face a problem, when I click a link button in my datagrid and the error message is like that Object Required :- javascript:__doPostBack('dgLookup$_ctl3$_ctl0','') Does anymore can help or give me a hint on this ?? Thank you...