validation error

if you add more than 2 page display with a nodereferrer relationship, view don't work and display a "validation error".

- use "nodeGalleryImage" and content type "page", with field_test_noderef in "page" where referenceable types is "nodeGalleryImage".
- in the content type nodeGalleryImage add a nodereferrer field vith referrer set a field_test_noderef.
- Load 2 immage: NGim1 and NGim2.
- Create 1 "page": page 1, where noderef field references NGim1 e 2.
- Set the same title for page and nodeGalleryImage
- Create a view based on nodes.
- Add a nodereferrer relationship by the noderef field in "page" (non-required).
- Add a field: title (do not use relationship), label "page node" and set "link to node".
- Add a field: nodeGalleryImage (attached to noderef relationship), label "image".
- Add a page display and another page display.

and work.

BUT if you add another page display, error validation.
where is my error?

(usefull module btw)