Hi,
That is strange.
You can edit the page by going to Administration > Add/Edit Pages, click on the page then click the wrench for page settings.
You might also try commenting out these in Web.config:
<add name="PageNotFoundHandler" type="mojoPortal.Web.PageNotFoundHttpModule, mojoPortal.Web"/>
<add name="PageNotFoundHandler" type="mojoPortal.Web.PageNotFoundHttpModule, mojoPortal.Web" preCondition="managedHandler"/>
and see if that changes anything.
Hope it helps,
Joe