This should fix your issue:
Line# 308
Replace
PHP Code:
$yourmessage=clean($yourmessage);
With
PHP Code:
$yourmessage=clean(nl2br($yourmessage));
Line# 326
Replace
PHP Code:
$message.="Content-Type: text/plain; charset=\"iso-8859-1\"\n";
With
PHP Code:
$message.="Content-Type: text/html; charset=\"iso-8859-1\"\n";