Module does not work. Notice: Undefined index: nid

Hi!
I am trying to get cnr working on my drupal installation.
I have a couple of custom content types of which one is a 'central' content type, i.e. a content type a bunch of other content types have a Node Reference field to.
I used to make use of the NodeReferrer module to get a back reference from the 'central' content type to the referrees.
Now I am trying to replace all NodeReferrer fields with NodeReference fields and use cnr to keep the mutual references up to date.
Unfortunately, every time I use the 'update existing nodes' function or edit a node manually, I get the following message:

Message Notice: Undefined index: nid in corresponding_node_references_update() (line 151 of drupal/sites/all/modules/cnr/corresponding_node_references.crud.inc).

No reference is updated afterwards. Did I do something wrong? Or am I missing something?

Here is my configuration:
Drupal 7.14
Node Reference 7.x-2.0
CNR 7.x-4.x-dev

Thank you very much!
llimit