Sandhya, You might want to check this post out:
<a href=http://exchange.ni.com/servlet/ProcessRequest?RHIVEID=101&RPAGEID=135&HOID=50650000000800000073C10000&UCATEGORY_0=_33_%24_12_&UCATEGORY_S=0>Real Time Feedback using NI 6025E</a> I believe it addresses the same issue. Good luck! If you have any further questions please post back. Craig H. National Instruments