Need help with javascript event handler

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C#

ASP.NET

Javascript

I have a dropdownlist on whose selected index changed a gridview get populated.
this gridview is placed inside an update panel.
for this same dropdownlist i have have put a javascript function onblur.
so onblur of this dropdownlist 2 textboxes get populated. these textboxes are outside the update panel.
Everything works fine..but i am having an issue wid the onblur...it works sometimes..and sometimes it does not work...
Please help