Which version of PHP are you using? Which version of CentOS?
This is the only place where apache_setenv is used
Code:
try {
// force disabling of g-zip so output can be streamed
apache_setenv('no-gzip', '1');
} catch(Exception $e) { /* ignore */ }
as you see it's setup to catch any errors.
My staging server runs CentOS 5.5 (with PHP 5.1.6), which has no problem with the datamapper code. Note that, as per the manual, Datamapper requires PHP 5.1.2+.