I installed Socialble v18.104.22.168 and have the same problem even though the More button is disabled, i.e. not used in my blog. The 32px by 32px more.png image file is missing in that directory per the plugin .zip release content.
The problem is it junks up the server logs with tons of 404 errors.
My solution is:
* Copy the more image on the Plugin Settings page using mouse Right Click -> Save Image As...
* Open the more.png saved image in Windows Paintbrush.
* Resize it to 32x32 pixels (disable the keep fixed aspect ratio)
* Save it to more.png
* Upload the more.png file to /wp-content/plugins/sociable/images/option1/32/more.png
* Check the file permissions are the same as the other icons in that directory. CPanel -> FileManager is really easy here.
This gets rid of the 404 errors although the more icon looks pixelated. You could easily fix that by some extra effort in Paintbrush but I just wanted to fix the 404 problem.
Overall, I like Sociable better than the super-options Share-and-Follow type plugins because it's simpler and doesn't drag in a lot of extra stuff that can complicate security and server load.