[imp] Warning: Cannot add header information - headers already sent by

[OUATTARA KARIM]

I installed Horde-imp.
- I renamed /var/www/html/horde/imp/login.php to login1.php
- I craeted a new Html page with images (Dreamweaver) and I saved it under login.php
- Then I included login1.php into login.php

When I load http://mysite/horde/imp I get this error message
 
Warning: Cannot add header information - headers already sent by (output started at /var/www/html/horde/imp/login.php:8) in /var/www/html/horde/lib/Secret.php on line 95

Can somebody help me? Thanks