Bug. Fail to move focus, add_comment.php

I have gallery embedded in phpBB.
In my configuration I have $gallery->app->comments_anonymous = "no"
In the code in add_comment.php line 156:

<script language="javascript1.2" type="text/JavaScript">
<!--
// position cursor in top form field
document.theform.commenter_name.focus();
//-->
</script>

Some of my users get error-message when trying to add a comment (error-message about fail to move focus, sorry - it is in norwegian).
I think this is because this field can't get focus in this situation (field now is read-only).