Header sent

Hi there,

I'm having an issue where this error message is displayed:

Warning: Cannot modify header information - headers already sent by (output started at /home/webencla/public_html/wp-content/plugins/domain-mapping/domain-mapping.php:338) in /home/webencla/public_html/wp-content/plugins/domain-mapping/domain-mapping.php on line 358

And then directed to a blank page with this page URL if I tried to logged out:

.(domain).../somerandomnumbers?action=logout&uid=10&build=20120917&follow_through=wp-login.php%3Floggedout%3Dtrue