Hello,
as regards 404 error, I can only direct you to
www.artio.net/faqs/artio-joomsef/trouble...er-clicking-any-link
I believe is was discussed here so many times, there is not much more to add. It is always the case issues causing it.
If this started to appear after you have updated your template, then check things possibly related to this.
First of all, check that your .htaccess file still exists and has correct values in it.