Recently migrated a Joomla 1.5 site to 3.3. Some but not all of my category blog links worked. It resulted in a “404 – Category not found” error. I would get various messages in the url. There would be “” or “ Private Message/thepageIwant.html”

I googled and found my answer here.

Basically delete the menu item and make a new one. Worked perfectly for me.

It gets better I found a “rebuild” button in the menu section. I checked the links that were giving me the 404 and they worked.

Hope this helps someone out there.