Turns out the answer is telling UAC to get out of the way.
Solution:
1. Click Start, click Run, type regedit, and then press ENTER.
2. Locate and then click the following registry subkey: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System
3. If the LocalAccountTokenFilterPolicy registry entry does not exist, follow these steps:
4. On the Edit menu, point to New, and then click DWORD Value.
5. Type LocalAccountTokenFilterPolicy, and then press ENTER.
6. Right-click LocalAccountTokenFilterPolicy, and then click Modify.
7. In the Value data box, type 1, and then click OK.
8. Exit Registry Editor.
Full details: [KB951016][1]
[1]: https://support.microsoft.com/en-us/kb/951016
