In Web.config you need to add some configuration for RAD Controls, in newer versions of mojoPortal these settings already exist but are commented out, so you just need to un-comment them.
For IIS 6 or IIS 7 with a Classic Application pool, you need to add this to the system.web httpModules section:
<add name="RadUploadModule" type="Telerik.Web.UI.RadUploadHttpModule, Telerik.Web.UI"/>
and you need to add this t the httpHandlers section:
<add verb="*" path="Telerik.RadUploadProgressHandler.ashx" type="Telerik.Web.UI.Upload.RadUploadProgressHandler, Telerik.Web.UI"/>
<add verb="*" path="Telerik.Web.UI.DialogHandler.aspx" type="Telerik.Web.UI.DialogHandler, Telerik.Web.UI, Culture=neutral, PublicKeyToken=121fae78165ba3d4"></add>
<add verb="*" path="Telerik.Web.UI.SpellCheckHandler.axd" type="Telerik.Web.UI.SpellCheckHandler, Telerik.Web.UI, Culture=neutral, PublicKeyToken=121fae78165ba3d4"></add>
For IIS 7 Integrated Pipeline Mode, yoy don't need the above but instead need to add this to the system.webServer modules section:
<add name="RadUploadModule" type="Telerik.Web.UI.RadUploadHttpModule, Telerik.Web.UI" preCondition="managedHandler"/>
and you need to add this to the system.WebServer handlers section:
<add name="Telerik.Web.UI.SpellCheckHandler.axd_*" path="Telerik.Web.UI.SpellCheckHandler.axd" verb="*" type="Telerik.Web.UI.SpellCheckHandler, Telerik.Web.UI, Culture=neutral, PublicKeyToken=121fae78165ba3d4" preCondition="integratedMode"/>
<add name="Telerik.Web.UI.DialogHandler.aspx_*" path="Telerik.Web.UI.DialogHandler.aspx" verb="*" type="Telerik.Web.UI.DialogHandler, Telerik.Web.UI, Culture=neutral, PublicKeyToken=121fae78165ba3d4" preCondition="integratedMode"/>
<add name="Telerik.RadUploadProgressHandler.ashx_*" path="Telerik.RadUploadProgressHandler.ashx" verb="*" type="Telerik.Web.UI.Upload.RadUploadProgressHandler, Telerik.Web.UI" preCondition="integratedMode"/>