@tig said:

First off ensure that SketchUp is installed [or repaired] correctly.
While logged into Windows as your normal user-account ensure that SketchUp is closed.
Find the SketchUp installer's exe file - usually in your Downloads folder.
Select the installer's exe file icon, right-click > context-menu > Run as administrator
When prompted choose Repair...
Restart your computer to see if that helped...

There is a way of forcing this, but is it's not so simple...

Here's how I did it myself...

You need to use Regedit - but don't use it if you are at all unsure !
Make notes as you go in case you need to reverse any changes...

Windows: Start menu > Run > Regedit > OK

Search for the string \ThumbsUp.dll in your various entries' Data settings...

Edit the entries that relate to the file-paths where the \ThumbsUp.dll is located...

They should all point towards the latest v2021 ThumbsUp.dll, rather than any earlier ThumbsUp.dll files that might exist in earlier versions' installed folders.

They should all read something like:
C:\Program Files\SketchUp\SketchUp **2021**\ThumbsUp.dll

Depending on how many versions of SketchUp you have installed it might take a while to find all of the paths and edit them...

After that ALL installed versions of SketchUp seem to make their thumbnail icons properly...
[You might need to restart your PC for the changes to be seen ?]

BUT surely this can be fixed 'properly' by 'the powers that be' at Trimble ??

IT WORKS !

You have to use the "Find" function in the Regedit. Then "Find next" and keep doing this until all entries lead to the SketchUp 2021\ThumbsUp.dll

It took me 2 years to find a solution for this. I lost so much time reading posts from the official "help" from the Sketchup stuff. Totally useless info. Thank you so much

I had the same problem. Rectangular vray light, inside component. I JUST RESTARTED SKETCHUP and the problem was fixed!

I just run the plugin in SU 2014 and works good