It was really great. Here the problem is i will not add items at client side. In my project i have to add items in to combobox dynamically as :
for(int i=0; i<3; i++)
RadComboBoxItem rcb = new RadComboBoxItem(i.ToString());
RadComboBox1.Items.Add(rcb); // RadComboBox1 is the name of combobox.
I tried to modify example which you have given. I have removed items part and added items as shown above. I was able to see the checkbox's for items but not the text of RadComboBox. When i have selected some of them and clicked button to display which items were selected then luckly i could see the correct items which i have checked.
The only problem is i could't see items text, but could see checkbox's for items. Hope you give some idea in this.