It sounds like includes/languages/YOUR_TEMPLATE/english.php (where YOUR_TEMPLATE is the name of your custom template) was incorrectly edited.

To remove the text, just remove the portion between the single quotes. If you remove the entire definition, files that use it will display the constant FOOTER_TEXT_BODY.

If the information in the footer used to read something like

Code:
define('FOOTER_TEXT_BODY', 'Copyright &copy; 2003-2006 <a href="http://www.zen-cart.com" target="_blank">Zen Cart</a>. Powered by <a href="http://www.zen-cart.com" target="_blank">Zen Cart</a>');
You should change it to
Code:
define('FOOTER_TEXT_BODY', '');
I changed the color of the single quotes to make it obvious that it's not a ".