How do I fix MSB3073 error in my post-build event?

Question

I\'m working on a project that requires that DLLs generated by building my solution to be copied from the bin folder to another folder, both of which are on my machine, in m

Answer 1

The Post-Build Event (under Build Events, in the properties dialog) of an imported project, had an environment variable which was not defined.
Navigated to Control Panel\All Control Panel Items\System\Advanced system settings to add the appropriate environment variable, and doing no more than restarting VS2017 resolved the error.
Also, following on from @Seans and other answers regarding multiple project races/contentions, create a temp folder in the output folder like so,

and select the project producing the preferred output:

and build (no rebuild/clean) is a speedy solution.