Forbidden You don't have permission to access this resource

I’m building locally on my Mac. I’m using the MAMP app to view my website locally.

It was all working fine, until I updated the Kirby folder, to the most recent version (I downloaded the Plain Kit and simply replaced the Kirby folder). Now when I visit localhost:8888 I get the following error message:

You don’t have permission to access this resource.Server unable to read htaccess file, denying access to be safe

Not sure what to do?

I’ve gone into the MAMP app Preferences and redone the Document Root (to the same location) and hey-presto it now works!