[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