My website has been working happily with GZip Compression enabled for over a year, but when I tried to disabled it the website stopped working ... Namely, it produced a clear screen with

Warning: Cannot modify header information - headers already sent by (output started at /home/matrecom/public_html/includes/languages/english/modules/shipping/bd/table.php:57) in /home/matrecom/public_html/includes/functions/functions_general.php on line 44

Enabling GZip Compression fixes this, but it must be something really wrong with my site to produce such an error! What would cause it and what would be required to fix it?

Many thanks,
Alex