Custom post type missing custom fields

Is display of the “Custom Fields” metabox enabled for your Custom Post Type’s Edit Screen?

To check:

1) Edit (Post Type) Screen
2) Click the “Screen Options” tab in the upper right-hand corner
3) Ensure the “Custom Fields” checkbox is enabled

WordPress 3.1 made some (ahem) decisions regarding which metaboxes should display by default on the Edit screens. In some cases, previously displayed metaboxes were changed not to display by default.