Calendar pop-ups not available in portal but appearing in BAB

Hi,

When I execute Sales Order transaction through BAB, certain fields with Date values are having pop up icon through which calender opens up, but same thing when executed through protal does not show such icon through which calendar can be opened, only the text field appears.

What could be the problem ? same thing I am executing

through BAB, it goes fine and in Portal its not showing

Vishal