This suggestion may be off the mark ... but ...
I have no problem at all with Windows 7 UAC on the second workstation.
On the first workstation when I was initally activating Windows 7 I had to give it an account name and it contained a typo.
At a little later date I created a new acdcount with Administrator proveledge (and no typo) and used it for all my processing.
I deleted the original account.
There was one folder in the Program Files folder that would not allow me to write because it apparently was created under the original account and UAC thought I was not approproatly credentialed to write to it.
Could this perhaps be the source of the original difficuylty?