Hello sudhir singh,
As I can see from the screenshot of your code - you use RadComboBox with Load-On-Demand.
When RadComboBox uses Load-On-Demand feature - RadComboBoxItems are loaded during callback
However the RadMenu is not able to register its scripts during callback and this causes the issue.
Let me suggest you avoid usage of Load-On-Demand in your case.
All the best,
the Telerik team