Note that the Telerik.Web.UI.DialogHandler.axd
HttpHandlers are usually registered in web.config as shown in step3 in the following help article: http://www.telerik.com/help/aspnet-ajax/moss-deploying-radcontrols.html
. Configuring them from the properties of RadEditor is not necessary unless your scenario requires it.
HttpHanlder is not related to RadEditor, it is used by the RadChart control.
As for RadStyleSheetManager, you just need to add an instance of the control on your page after the ScriptManager:
You can find more information about this control in the following help article: http://www.telerik.com/help/aspnet-ajax/stylesheetmanager.html
If you are still having difficulties after checking the information above, clarify which version of the Telerik controls you are currently using and in which browser you are viewing them. If possible open a support ticket and send a fully runnable sample that isolates the problem at hand so that I can inspect it locally and provide a more to the point answer.
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