In some cases it can be quite useful to share static content between different web applications. A way of achieving this is to include the files in a dll as embedded resources and serve them using a custom VirutalPathProvider, for most things this will work without any additional work. However if you are using dotless to make your css more maintanable you need to do reconfigure dotless to work with files served from a VirtualPathProvider. The 2 small changes you need to do in your web.config are, under system.webServer > handlers change the value resourceType attribue from File to Unspecified.

<add name="dotless" path="*.less" verb="GET" type="dotless.Core.LessCssHttpHandler,dotless.Core" resourceType="Unspecified" preCondition="" />

And in the dotless configuration section add a source attribute with the value dotless.Core.Input.VirtualFileReader.

<dotless minifyCss="false" cache="true" web="false" source="dotless.Core.Input.VirtualFileReader" />

Also make sure that there's no static added under system.webServer > handlers for the less extension.