Thanks for the fast reply!
When pasting the code on a new page on an external page it works. (yes!)
But I would like to add the subscription form on the sidebar of an external web site by a Widget. (I used a text Widget)
When I submit the form I get a blank page and it ends at wp-comments-post.php
Any solution for this problem? (do I have to alter the subscription form code when using the sidebar Widget or am I using the wrong Widget (text) or should I maybe add the subscription form code in the sidebar.php?
Thanks again!
Martijn