Thank you again mc12345678 and wmorris.
It appears you were correct in surmising that the EASYPOPULATE_4_CONFIG_TEMP_DIR is missing.
See the screenshots that I took after using the "un-install EP4" button:
Click image for larger version. 

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Click image for larger version. 

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I'll do as you suggest, add the file, and redo the un-install and re-install.
Where should the file be inserted, just to make sure I put it in the correct place?
Thanks again. I'm looking forward to using this great add-on once again. It's such an awesome tool!