it seems that one or more of the resources has not been added properly to the page. However, I could not tell why exactly. It could be related to IE 31 CSS limitation (if this happens in IE only), or something else.
To be able to help you further, we will need a working sample of your project, so we could test it locally on our machines. Open a support ticket, and send us your project in order to provide further help.
You could also try to remove the following line from your code to check if it gonna work:
When you use custom theme, usually you should not disable the base CSS file, but only the skins specific. Base CSS file controls the main layout of the controls such as floats, margin, padding etc. If it is disabled, it is possible to have the skin specific styles - colors, background colors etc. but the controls to be with a broken layout.
All the best,
the Telerik team
If you want to get updates on new releases, tips and tricks and sneak peeks at our product labs directly from the developers working on the RadControls for ASP.NET AJAX, subscribe to their blog feed