External Java script not called while calliing it from a control inside modal popup.

Hi Friendz,
    I am getting an error while calling a javascript from a dropdownlist which is placed inside a modal pop-up panel. if i am ebeding a small script like onchange="javascript:alert('hello');", it works fine. But if i m using <script> </script> for embeding  a javascript its showing 'object doesn't support this property' error. when i debugged it the compiler does not get into the javascript function.
Below is a screenshot of that page.
fast reply awaited.




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