Most likely the antivirus, that must have blocked the installation of the latest installer, which downloads the operator thumbnails as part of the update.
Configure the antivirus to add the whole Addon Manager folder to the EXCLUSIONS
Run the FSDT Installer again, and choose Update
If that doesn't work, try to install the OFFLINE installer on our site, then start the Installer again, and do another Update Check. Pay attention to the update process, and see if the operator Thumbnails are being downloaded.