my MyLogin.html looks :
<html>
<head>
<title>Unbenanntes Dokument</title>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
</head>
{header}
{user_box}
{footer}
<body>
</body>
</html>
You are close but you did not follow the instructions I gave exactly.
The file should contain ONLY:
{header}
{user_box}
{footer}
The contents of header.html and footer.html will contain the <HEAD> and <BODY> tags. If you add them again, you will produce a page that contains invalid HTML markup.
Try again with only the 3 lines as I have illustrated and it should work. I tested it this way myself before making my first post.
(Of course you can also ADD additional body content as you see fit)