I work with Rob, and I have been nutting this out tonight and have the solution, so here is an answer that may work for others:
I followed Martin's advice in anoter forum note, and checked out the source code of the non-appearing graphic. The path was wrong. I changed the variable setting slasharguments to the ? (rather than /) option, and bingo.
Checking the response just above mine that came in just ahead of my post i note this this is a second best moodle workaraound to an IIS problem. I will work with Rob to change the windows server settings as an alternative and let you know how we go if we get results.