Error: Undefined index (fix)

This error shows up when I'm in debug mode on IIS 7.5 on Windows Server 2008R2 and WordPress.

Notice: Undefined index: custom_fields_block in D:\HTTP\www\wp-content\plugins\custompress\core\content-types.php on line 691

Here's how I fixed this - I added this line to 691:
if (isset($this->post_types[$object_type]['labels']['custom_fields_block'] ))