Is the navigation control you are using a custom one you created or it is the navigation widget built in in Sitefinity?
If it is a control you created can you send it to inspect the problem?
Do you have your pages created with the option show in navigation?
Try to view the page where is the control with Firebug ON to see if some error appear or if some resources do not get loaded and are stuck.
the Telerik team
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