If you're still struggling with this, I found that I received the same error when I had VISION-DETECTION set to TRUE instead of True. For some reason having it in all caps made it not work for me.
Hope you get it working!
After reading New to LPR? Considerations Before You Begin I'm thinking I'd like to buy a Dahua HFW5241E-Z12E to capture license plates down my street.
I'm just getting into home security so I still have a lot to learn. If there is a better model you would suggest for this use case...