Sheet set plotting with page set-up override

Most of the time when I use Sheet Sets I have the option "publish using page set-up override" so I can select one of a number of plot options.
Occasionally though I find a particular sheet set has the "publish using page set-up override" greyed out.
Why is this available on most of my sheet sets but not on all?
I am using ACAD 2007.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
Add image file
Upload is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.