hi,
I checked the LightMart default_pricelist.php file on my localhost. Line 57 can't generate any error message, because literally there is nothing on line 57 in terms of PHP. Did you touch that PHP file that switches the line numbers?
If you do, get the original default_pricelist.php from the LightMart installation file, and tell me the official line number so i can test it out on my localhost.
regards.