Recently, Adobe updated the flash player to version 11.5, and this spawned a few problems. With Imagevue, it caused thumbnails in the main menu and also in the thumbnail-scroller to disappear (see related topic).
We have now fixed this issue with a workaround, and you can get the latest release in the Imagevue downloads section. Here are the official release notes:
https://www.photo.gallery/updatelog/imagevue-x2-8-5/
If you don't have time to do a full upgrade, then at least replace the /iv-includes/imagevue2.swf file on your server, as this will fix the thumbnails issue (requires version 2.8.4 or newer).
* After upgrade, make sure to empty your browser cache so that the new version loads from your server.
For those of you who are interested in knowing more about the technical background of the issue, it is related to an event failing to initiate on loaded JPG files. Since Imagevue could not initiate the given event, it also failed to change the opacity of the loaded image from 0 to 100. We have now worked around this issue of course. Read more:
http://forums.adobe.com/message/4844945