1. Downloaded your application (mymulticombo.zip)
2. Added the latest dll files (Q3 2008 Beta)
3. Created a virtual folder (called mymulticombo) in IIS which points to the application. Then I added default document for that virtual folder to be search.aspx
4. I opened the http://localhost/mymulticombo/ URL in the browser and the page worked fine. All the comboboxes were fine.
What is different in your case?
the Telerik team
Check out Telerik Trainer, the state of the art learning tool for Telerik products.