That indicates the icon handler dll file is missing or damaged, I suspect. Best way to fix it is to reinstall.
An employee at my office is having the same issue in a similar form: the icon was initially viewable, then because Windows default, I uninstalled and reinstalled the program and the icon was then viewable again then, in a seemingly random manner, it became Windows default again. I figured uninstalling and reinstalling would solve the problem again but unfortunately this time it did not.
I thought perhaps determining which DLL it is that generates the thumbnail and then registering it might make a difference.
Can you help?
Thanks Peter, I didn't end up having to do the reinstall, there was an update for inDesign that solved the problem and brought the icon back.