Linked page gives "object does not exist" message

Hi,

I'm trying to add a linked page in one site that is linked to an existing page in another site.

The linked page appears to be added successfully but the Form tab just displays "The object does not exist. It may have been deleted by someone else."

There's no indication which object it is referring to, and the logs don't provide any information. It appears to be caused by the fact that I'm linking a page across sites because page linking seems to work fine within the same site.

Any ideas? Thanks.