Sorry but is your plugin changing code in files automatically?
After 1-2 admin requests, the I10n.php is broken because of this:
if (!function_exists('__')) {
function __( $text, $domain = 'default' ) {
if ( defined( 'M2I_MAGE_DIR' ) && class_exists( 'M2I_External' ) && M2I_External::$needs_mage_translate ) {
return M2I_External::translate( func_get_args() );
}
}
else {
return translate( $text, $domain );
}
}