Hello Tho Shi Teng,
The code that you provided is not enough so we can reproduce the issue locally and inspect where the issue comes from. Since the problem that you encounter is very customized one I would suggest that you open a support ticket and send us a
runnable simple project that demonstrates the issue.
Greetings,
Kate
the Telerik team
Register for the Q2 2011 What's New Webinar Week. Mark your calendar for the week starting July 18th and book your seat for a walk through of all the exciting stuff we will ship with the new release!