For me, it seems tied to Gatekeeper. If an application or kernel extension needs to be allowed, it often seems to break and give that Security & Privacy error every time I attempt to go in. Clearing out the preferences files (via defaults delete or otherwise) mentioned by others doesn't help -- nor does rebooting or logging in as a different user -- but leaving it alone long enough for Gatekeeper to time out on those allow requests seems to resolve it. Unfortunately, that means you can't open any apps that are prompting for it or add any kexts, it seems. I have gotten some to be allowed because it doesn't always seem to happen. Hoping they fully fix it in the next beta.