I have this same problem in Ubuntu 16.04 and tried the same fix but it didn't work.
It might be worth noting that my error says "System.DllNotFoundException: FreeImage"
I'm not sure if this is a difference in how libraries are loaded in the different Ubuntu versions, or if this is a sign that the error is actually slightly different.
EDIT: I think I made the stupid mistake of trying to use my WindowsGL build on linux. That would explain why it's referencing the dll name, FreeImage, rather than the the lib name. I decided to just stick with a single dev environment (Windows) so I don't need to maintain multiple sets of framework and pipeline packages. I can just copy the DesktopGL build from Windows over to Linux whenever I want to test on Linux.