when I click on sandbox I get the following error:

Fatal error: Access to undeclared static property: plgSystemDemo::$activeViewLevels in /home/cook/sites/www.j-cook.net/public_html/sandbox/cms16/administrator/components/com_demo10627/demo10627.php on line 43

It is working now, but still it can fail. I am triing to fix that now.
The problem is at the sandbox reinstallation. It passes for all sandbox, but 1.6 I have strange problems.

I am gonna check closer every day the flushing of the sandbox, and what can be disturbing it.

Anyway, it is working in your localhost. So for sandbox, your can use 1.7 for the moment wich is graphically the same.