I could solve the problem by adding the php-function “post_password_required()” (found in codex).
if (!post_password_required()) {
wp_link_pages(array(
'before' => '<div class="pagelink">',
'after' => '</div>',
'next_or_number' => 'next_and_number',
'nextpagelink' => '<div class="nextpage">'.__('→').'</div>',
'previouspagelink' => '<div class="prevpage">'.__('←').'</div>',
'pagelink' => '<div class="number">' . __('%') . '</div>',
'echo' => 1 )
);
}