Since I updated to version 6.5 I can create pages from a parent node without problems, but, it's not letting me create a page in the case where the parent has more than one offspring of nodes. The funny thing is that if no child node has been created, a new page can be created without problems, but once a new page is created, no more can be created.
I have almost used all 6.5.x versions and never faced this issue. Something might be missing here, could you provide your content tree and jcr:content of each node to further look into this?