As I understand it, User Access Control, or UAC, can basically intercept requests for your group membership so in this case, it appears it was preventing your membership getting passed to SQL Server.
Others have noted in their comments that you may still need to right click and run SSMS as an Administrator.
As noted by an astute observer “This is a quick-fix, not a real solution. People shouldn’t just be running stuff as administrator. These security walls are in place for a reason” And I agree. UAC is designed to get Windows users into a Principle of least privilege mindset – only escalate to a powerful account when required. The issue is that SSMS is known to not “play well” with UAC. As I see it, this leaves you with three options
- You can turn off UAC and get your work done
- Leave UAC on and tell your boss you are unable to work
- Write your own query tool that is not affected by UAC