Floss Your Mind » Blog Archive » Weird Problem with Vista User Access Control (UAC)

Weird Problem with Vista User Access Control (UAC)– solved

June 19, 2008 11:22 pm Raffi Enterpise, Vista

I came across an issue with Windows Vista recently at a client that had been dogging me for quite some time.

Fortunately, most of the client’s PCs here in New York run Windows XP, but one of the principles wanted a Tablet PC and I figured that Vista’s Tablet integration was much better than the specialized Windows XP Tablet Edition.

Although the client admin rights on his own laptop, each time he tried to install an application, the typical UAC dialog box would come up. The installation would continue and then would quit with an error trying to access the H: drive.

Well, the only H: drive that the client had was his network home directory. Why would the installer need access to that drive? The client had that drive mapped so it should have worked right?

The workaround for the past few months was to log in as a secondary local account on the computer in order to install applications. Of course this was a pain, but it minimized my time on the computer and at the client’s site so it was a win/win for both of us. Finally one day I was determined to figure out what was going on.

I couldn’t find anything in the registry, so I ran the Command Prompt as Administrator by Right-Clicking the Command Prompt shortcut and selecting “Run As Administrator.” This explicitly tells the computer that you’re running as full admin without the UAC stuff going off. However, this
“Run as Administrator” acts like a new account. The install still failed, but while looking around in this environment through the command prompt, I found the drive letter H: was not mapped. After mapping the drive letter, the install worked.

Ok, so now I know why it the install fails. When the privilege escalation takes place, the profile no longer has access to that H: drive. But why does it need the H: drive? It turns out the client was redirecting his My Documents to his home drive using a Drive Path setup (H:\My Documents) rather than UNC (\\server\homeshare\username\My Documents). By changing the redirection to use UNC paths, the problems went away for all installations.

Weird oddity, but interesting none-the-less. I’m wondering how this affects other installations particularly environment variable changes or registry changes.

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