migration to new host: Export sends wrong headers

I configured Hikashop on one host and then moved to another one.
At the first one all worked well, on the new one when press product "Export" instead of the .CSV I get several Warning messages:

Warning: Cannot modify header information - headers already sent by (output started at /MY_PATH_TO_JOOMLA_FOLDER/plugins/system/hikashopuser.php:21) in /MY_PATH_TO_JOOMLA_FOLDER/administrator/components/com_hikashop/views/product/tmpl/export.php on line 355

PHP Version 5.2.5

System Linux SERVER_NAME 2.6.9-67.0.1.EL #1 Wed Dec 19 15:50:25 EST 2007 i686
Build Date Mar 13 2008 04:37:09
Configure Command './configure' '--disable-pdo' '--enable-bcmath' '--enable-calendar' '--enable-exif' '--enable-ftp' '--enable-gd-native-ttf' '--enable-libxml' '--enable-magic-quotes' '--enable-mbstring' '--enable-sockets' '--enable-zip' '--prefix=/usr/local' '--with-apxs2=/usr/local/apache/bin/apxs' '--with-curl=/opt/curlssl/' '--with-freetype-dir=/usr' '--with-gd' '--with-gettext' '--with-imap=/opt/php_with_imap_client/' '--with-imap-ssl=/usr' '--with-jpeg-dir=/usr' '--with-kerberos' '--with-libexpat-dir=/usr' '--with-libxml-dir=/opt/xml2/' '--with-mcrypt=/opt/libmcrypt/' '--with-mysql=/usr' '--with-mysql-sock=/var/lib/mysql/mysql.sock' '--with-openssl=/usr' '--with-openssl-dir=/usr' '--with-png-dir=/usr' '--with-pspell' '--with-ttf' '--with-xmlrpc' '--with-xpm-dir=/usr/X11R6' '--with-zlib' '--with-zlib-dir=/usr'

PHP Version 5.2.17

System FreeBSD SERVER_NAME 8.2-STABLE FreeBSD 8.2-STABLE #0: Fri Sep 30 22:32:51 MSD 2011 amd64
Build Date Oct 31 2011 15:13:21
Configure Command './configure' '--with-apache=../apache' '--enable-dbase' '--with-mysql=/usr/local' '--with-pdo-mysql=/usr/local' '--with-mysqli=/usr/local/bin/mysql_config' '--with-pgsql' '--with-pdo-pgsql' '--with-pdo-sqlite=/usr/local' '--with-gd' '--enable-gd-native-ttf' '--with-ttf=/usr/local/lib' '--with-freetype-dir=/usr/local/lib' '--with-gettext' '--enable-magic-quotes' '--with-xsl' '--with-libxml-dir=/usr/local' '--with-imap=../imap/' '--with-imap-ssl=../imap/' '--enable-force-cgi-redirect' '--with-mime-magic' '--enable-sysvshm' '--enable-sysvsem' '--with-zlib' '--with-curl=/usr/local' '--with-iconv=/usr/local' '--with-bz2' '--with-jpeg-dir=/usr/local' '--enable-calendar' '--enable-ftp' '--enable-mbstring=all' '--enable-soap' '--with-openssl' '--with-mcrypt' '--enable-zip' '--enable-inline-optimization' '--enable-exif' '--enable-sockets' '--enable-bcmath' '--with-xmlrpc' '--with-ming' '--with-imagick' '--with-mhash' '--enable-exif' '--with-t1lib' '--with-tidy'

SOLVED
Deleted empty string between <?php tags in /MY_PATH_TO_JOOMLA_FOLDER/plugins/system/hikashopuser.php