I recently attempted to remove RC code from a semi-production server this weekend and noticed I was getting errors from the 'Web Components' and 'Core' installation bits. The errors indicated there was a permission issue which wasn't much help.
Eventually I figured out that UAC in Windows 2008 was preventing me from removing OCS and I quickly turned it off on all my servers. This raised another issue though....
When attempting to install and activate the various OCS R2 components afterward I noticed the pre-requisite checker had indicated items such as 'Prepare Active Directory' where listed as 'Complete' however no checkmark appeared next to the words like it normally does. It was also greyed out.
The fix took a few minutes to figure out but at the root of this issue is the fact that the OCS setup page is an HTA (application) and Microsoft's Internet Explorer Enhanced Security was getting in the way. After disabling this feature I was able to continue installing the RTM code for OCS R2 :)
Hope this helps someone else out there!