filrancan on "Errore 404"

Hi,

hi have an error 404 on all my posts.
I'm not sure but might be since i updated to 3. (site is on the making).

Here an example
http://www.stampantitred.it/storia-delle-stampanti-3d/

I might have to change the htaccess permission, I guess reading around, but i did not understand if it's the correct solution, and how to do it...
So far I'm capable of changing some text in the htacces.

Many Thans

F