Getting an "undefined index" error in trying to register a form using the "field collection" module

Was hoping to reorganize fields within a "field collection" set. (Module: http://drupal.org/project/field_collection)

If you're not familiar with the module, you essentially create a sub-form to group fields into sets. If I try to register either the field collection or the content type containing the field collection, I get this error:

    Notice: Undefined index: #pre_render in rel_form_alter() (line 293 of /sites/all/modules/rel/rel.module).
    Warning: array_merge(): Argument #2 is not an array in rel_form_alter() (line 295 of /sites/all/modules/rel/rel.module).

If it's not really a bug, but an unsupported feature, I would really appreciate this module's accommodating the field collection module.

Thanks.