Taskbar Preview Missing

[ct202s13stu2]

When I hover over taskbar Dexpot icon, I do not see preview of the four desktops. I checked this:
Open 'Settings > Plugins and Extras'. Click 'SevenDex' from the plugin list.

It has been selected.

Thanks for your help

[Patrick]

Do you get a list of desktop names instead? The preview images only work when the Windows Aero Theme is enabled.