How to fix 'Runtime critical type System.Threading.InternalThread not found' ?

After installing Unity and creating an empty project, I see the following error in the console:

‘Runtime critical type System.Threading.InternalThread not found’

I have tried Unity versions 5.6.1f1 and 5.6.2f1 with the same result. I have also tried uninstalling and reinstalling Unity. I have also tried the 64 and 32 bit versions. I have tried restarting my computer. I seem to always get this error.

It seems that there is something on my system that interferes with the installation.

Does anyone have any ideas about what could be causing this?

Removing the “MONO_PATH” environment variable fixed it.

I noticed in the editor logs that this path was being used during compilation. My coworkers computer did not have this entry in his unity editor log file. So, I tried removing the environment variable from my system and the problem went away.