Hi,
First, I recommend you upgrade to mojoportal 2.3.0.8. There were some issues in 2.3.0.4 which led to a soon update to 2.3.0.4.b so its possibly related to issues that have been fixed.
The only thing I can think of that would cause those log errors/page not found errors is if you initially were creating pages using http://localhost/ and later changed it to a virtual directory like http://localhost/mojo/, then the urls in the mp_FriendlyUrls table are not correct because /home.aspx is not the same as /mojo/home.aspx
and friendly urls map to a real url but if you change the structure of the url after creating some pagesw then the real url may be /Default.aspx?pageid=x when it really needs to be like /mojo/Default.aspx?pageid=x
Hope it helps,
Joe