It happens from time to time, and there doesn't seem to be any real reason for it that I've been able to discern. Normally I'd think it's just some old program or installer, but this happened with the latest Mozilla Firefox for me once.
Sometimes it works if you right click a file and then select "Run as Administrator", but other times not. Probably the best thing to do is what you did, and make a new account since my working theory is that this is an early sign of profile corruption. Which is why it's always good to have a "spare" admin account you can use if things go south.
I recently got myself a Dell studio 15 with Windows 7. First start up went ok, entered in the details to create an account as and when it was asked. However, when it came to installing some programs it told me I needed Admin privileges to do so, however my account was an Administrator type (verified in Control Panel>User accounts)!
I then created a new account, made it Administrator as well, then deleted the first account. This seems to have worked, but because I'm unfamiliar with Windows 7 I'm not 100% convinced that I can full Administrator privileges. Has anyone experienced something similar and know how to verify that the account is truly fully Administrator?

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