All portfolio items redirect to 404 page?

Hey aybekdes!

Go to your WordPress settings>Permalinks and then set the option to default. After saving test your portfolio pages and see if they show up correctly.

If they do, make sure that you have the portfolio slug names set to names that are not used *anywhere* else on the site for any other pages slug. WordPress will not work when pages have the same slug.

If even with the default settings (portfolio, portfolio-item) its not working with custom permalinks set then you would need to try the permalink troubleshooting options mentioned on the WordPress codex here: http://codex.wordpress.org/Using_Permalinks#Fixing_Permalink_Problems

Best regards,
Devin