Somehow I can't add reviews in the front-end of my Magento installation.
Initially I also wasn't able to add them in the back-end as well (404 error), but I resolved it with this tread: https://stackoverflow.com/questions/22846783/magento-admin-screens-add-new-review-button-not-working-and-generates-a-404-erro . So after this fix I can add them in the back-end and they show up in the front-end.
But now 1 problems remains. When I fill out the forms on the front-end and I hit 'Submit review' nothing happens. I hope someone can help me out.