Zoning ordinances and permits are very prickly things. Running a retail business that has some foot traffic is very different from running an event space where you can expect larger groups to congregate. And where more people congregate, there's more risk of people getting hurt, starting a fire, or causing mayhem on the surrounding sidewalks, etc.

Each locality has its own rules and regulations concerning the license to assemble/right to assembly (which has to do with people gathering, not putting parts of a machine together). If you don't have a food establishment permit, or you're in the wrong zoning area for your art gallery/live music, that could be the reason for the fire marshal's reaction.

To get to the heart of the matter most quickly, speak to an attorney in your area who deals with small businesses like yours -- they'll likely know exactly which permits you need and how to file them expeditiously.