Long version.
My domain was xxx.com
i shut that domain down and made yyyy.com
The sessions paths are written when you do a import / install.
Because i just uploaded my forums, the sessions path was never changed. And the problems came to light when what was the xxx sessions folder was deleted.
So rick dived into a file and modified it.
That resolved it.
I would normally post the hows n whys but it cost me a support ticket

But like i say if you move install, not just download upload.