Hi ... One of the original errors changed a little, but the problem remains ... let me explain. 
When I chose the 'site offline' action, an error message was thrown and a template default image was presented, basically advising me there was an error. 
One of your colleagues had a look at teh problem and later suggested I have a look. When I looked I noticed the default image is no longer there, instead I get a browser message suggesting the site does not exist. And I am unable to access the site and work offline. 
So I have to deactivate the site offline. This means the site is live while I work on it.
It appears that the path between setting the site offline and the target offline.php is incorrect
All others appear to be resolved although these seemed to be user error.