Strange error with a "Contact Us" form after adding a Google map

I have a Contact Us form with server validation and email facilities. The form works as it should. Emails are sent, I'm redirected to the "Thank You" page and if I forget to fill in a required field, the server validation alerts me. So far so good.

I have also added a Google map to this page. The Google map works fine, but the form does not. Emails are sent, but I'm not redirected to the "Thank You" page and the server validation creates this error:

Warning: session_start() [function.session-start]: Cannot send session cache limiter - headers already sent (output started at /home/4/s/syversen-elektro/www/kontaktoss.php:1) in /home/4/s/syversen-elektro/www/webassist/form_validations/wavt_validatedform_php.php on line 3

Warning: Cannot modify header information - headers already sent by (output started at /home/4/s/syversen-elektro/www/kontaktoss.php:1) in /home/4/s/syversen-elektro/www/webassist/form_validations/wavt_scripts_php.php on line 83

You can test it on live URL here:

kontaktoss.php

I'm attaching my working files.

Regards
Rune