Fatal Error after creating Custom Display Suite layout
Have a look in the code for Display Suite, specifically the block mentioned in the error message:

function _ds_layouts_scan_theme($theme, &amp;$layouts) {
  $theme_layouts = file_scan_directory(drupal_get_path('theme', $theme) . '/ds_layouts', '/inc$/');
  foreach ($theme_layouts as $file =&gt; $values) {
    include_once(DRUPAL_ROOT . '/' . $file);
    $function = 'ds_' . $values-&gt;name;
    $layouts[$values-&gt;name] = $function();
    $layouts[$values-&gt;name]['path'] = str_replace('/' . $values-&gt;filename, '', $file);
  }
}


Note that when it goes looking for layouts is it prepending your layout name with 'ds_'.  

I imagine this is to prevent functions being included that were not intended for this purpose, a bit like using your module name in place of hook_ when you implement hooks.

That's why changing your function name worked.