Using Node Builder clears queue

First up, I've just discovered Node queue, and this is a great add on.

I'm afraid, however, its not working for me.

Node Queue is functioning fine, I can add and remove nodes from a queue, re-sort etc.

However, every time I use Node queue, it clears out the queue [if there is nodes listed], and doesn't add any nodes.
After using the queue builder screen, the nodequeue admin screen at /admin/content/nodequeue says that 1 item is listed, but when you click on the 'view' link, it is empty.

I'm pretty sure I've followed all the instructions given.

I've been careful to only add the correct node types to a particular node.

Any clues on what to test, to get this working?

Regards
Alan