You should write the fully name only if you store the Telerik.Web.UI.dll in the GAC. In your scenario it seems that the Telerik.Web.UI.dll file is placed in the bin folder so you can use the short names:
<add verb="*" validate="false" path="RadScriptResource.axd" type="Telerik.Web.UI.RadScriptResource, Telerik.Web.UI"/>
<add verb="*" validate="false" path="Telerik.Web.UI.DialogHandler.aspx" type="Telerik.Web.UI.DialogHandler, Telerik.Web.UI"/>
<add verb="*" validate="false" path="Telerik.Web.UI.SpellCheckHandler.axd" type="Telerik.Web.UI.SpellCheckHandler, Telerik.Web.UI"/>