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To provide better File Upload experience and usability, starting from Q3 2012, RadAsyncUpload is enabled out-of-the box in RadEditor's File Browser dialogs. Therefore the handler for the AsyncUpload should be registered in the web.config explicitly:
<httpHandlers> <add path="Telerik.Web.UI.DialogHandler.aspx" type="Telerik.Web.UI.DialogHandler" verb="*" validate="false" /> <add path="Telerik.Web.UI.WebResource.axd" type="Telerik.Web.UI.WebResource" verb="*" validate="false" /></httpHandlers> ...
<handlers> <add name="Telerik_Web_UI_DialogHandler_aspx" verb="*" preCondition="integratedMode" path="Telerik.Web.UI.DialogHandler.aspx" type="Telerik.Web.UI.DialogHandler" /> <add name="Telerik_Web_UI_WebResource_axd" verb="*" preCondition="integratedMode" path="Telerik.Web.UI.WebResource.axd" type="Telerik.Web.UI.WebResource" /></handlers>If the Telerik.Web.UI.WebResource.axd handler is not registered AsyncUpload will not function correctly and the File Browser (ImageManager, DocumentManager, MediaManager, etc) dialogs will look in a similar way:
Both Telerik.Web.UI.DialogHandler.aspx and Telerik.Web.UI.WebResource.axd handlers can be registered in the web.config file via the RadEditor's smart tag.