In general when using the
in your application the paths set in the web.config file need to be relative to the root of the application as explained in the Serving external style sheets
help article. Also when you register the stylesheets in the RadStyleSheetManager the paths to the files can be relative to the root or to the folder containing the current page
. Please take a look at the above mentioned help article and in case this does not help I would ask you to open a support ticket where you can attach a very simplified runnable project so I ca test you scenario locally and help you out.
the Telerik team
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