Vista UAC / Drive Access Denied

I just got done rebuilding a couple of my machines on Vista64 sp1 with .NET 3.5 SP1 and the works.   On my desktop, I tried to go view some of my photos.  As soon as I clicked on the drive I get a "Access Denied".  After a quick panic attack, I went to the disk manager and the drive looked fine and check disk ran ok, but I still would get "Access Denied" trying to view files on the volume. 

After not having any luck there, I rebooted and did all the typical stuff even tried the built-in admin account instead of my domain account and still no luck.  I had a full backup before the rebuild that's on my on-line backup but still it was driving me nuts!

After some searches I found some people talking about UAC causing that.  Sure enough, I had been trying really had to leave UAC enabled even though being prompted 946 times (ok, I exaggerated a few times) during the install. ok, so the real reason I wanted to leave UAC on was so I could have full use of Live Mesh which currently requires it active for anything but basic file sharing.

Not needing another excuse to kill UAC, I promptly turned it off and rebooted and sure enough the drive access denied message was gone I could access my files.

So what the heck?  anyone know why UAC causes drive access issues?