Not really, it's a page named Download, and I want to add it as a parent for another one. I really have no idea why only that page causes this... and it's case sensitive, again, the only one.
If I add other pages as parent everything works fine. I tried deleting it and adding it again, no chance, nothing works..
And on top of this I did a test today : added a page test and added that as a parent for page test 1 and everything worked fine.. why the Download page won't allow this is beyond me ..
I tried deleting the pages and adding them with lower case letters, again, this did not work..