wp_nonce not working: are you sure you want to do this…

Hello,

i’m having problems with the wp_nonce..

so i have a custom meta box
in which i have
wp_nonce_field( $this->slug . '-nonce-meta-test', $this->slug . '-nonce-test' );

slug is something like ‘wp-plugin’

and then in my save_post method i have

wp_verify_nonce( $_POST[$this->slug . '-nonce-test'], $this->slug . '-nonce-meta-test')

but it fails everytime and shows are you sure yo uwant to do this bla bla..

Any ideas what i’m doing wrong?

Thanks in advance