Is the DataSource declared in test1.aspx? If it’s a global set in the page that launches the popup, then it will not be in scope for the new window. You can pass it as the second “args” parameter to showModalDialog.
Does your DataSource reference an absolute URL or a relative one? Is the DataSource actually getting its data in the first place? If it’s a remote source on the same domain try making the reference a path from root if you are using just the file name.