configSource Attribute

A Web.Config file's configuration section can optionally specify a separate file to define configuration settings. The section should not have extra content in this case, and the external file is specified via the configSource attribute. If the configSource attribute is specified and the section contains content, a compilation error occurs.

        <httpHandlers configSource="Configs\myHttpHandlers.config">

DevExpress components automatically insert special elements (HttpHandler and HttpModule) in the base Web.Config file. Since this can result in a compilation error, tags with the configSource attribute are skipped without writing anything to it.

Note that in this case you should upgrade these sections manually. Refer to the ASPxHttpHandlerModule topic to learn how to do this.