@kristarella – thanks for the feedback and proposed resolution, but I’ve tried everything you mentioned and the image upload is still not working properly. I’ve remove Super Cache (via FTP), deactivated all plug-ins, cleared cache, tried alternative browsers. Also of note, the other 4 sites I manage with WordPress do not have this issue at all (all on the same hosting service – Network Solutions).
Any other ideas?
@nallejacobsson — I will take a look at the details of the other post, but from what I can see this will require me to change WP delivered code, which I would like to avoid. If this is a WP issue, then there should be a patch delivered.