I had a problem with Bulletproof Security blocking the Add Gallery button as well.
Adding the code above to the .htaccess file didn't work, and neither did adding it via the Bulletproof Security plugins settings.
Eventually, I figured out that if I temporarily turn off the Bulletproof .htaccess file in the root directory (reverting back to the WP default), I was able to run the plugin to create my gallery, and then turn Bulletproof back on once I inserted the gallery.
I don't change my galleries more than once or twice a year, so this is a decent workaround for me. I imagine if I was changing galleries on a daily basis, I'd probably want to come up with something better.