What i found was. When i'm using “Teeny Rich textarea”-option then the enters are working. Is there a way to disable certain buttons in the texteditor-toolbar? I don't want my visitors to put links and quotes in theire posts.
When you are printing the value, you need to use something like this: <?php echo nl2br( get_post_meta( $post->ID, 'your_meta_key', true ) ); ?>. The nl2br() function will convert the new lines to html line breaks.
You can remove certain buttons, but that will require editing the plugin, which is not recommended.