Thank you Jeremy for the quick reply!
That is the URL the 404s are related to as shown in a snippet from the security log above. And you're right, deactivating the Ozh plugin cured the problem, so thank you a ton. :)
The fact thought that I had also stopped the 404 errors by deactivating Jetpack suggests that there is a possible degree of conflict between Jetpack and the Ozh plugin. Has anyone had a chance to discuss this with the Ozh developer?... because that is one sweet little plugin, giving users about 20% more window or desktop to play with. Are there any other similar plugins you suggest which perform the same function as Ozh?
Is the post you linked to suggesting a work around by installing a cache plugin?
http://wordpress.org/support/topic/404-causes-from-add_menu_page-icon-with-div?replies=1
Anyhow, thank you again for your help.
Cheers,
Randy