Microsoft has identified an issue with the Windows 7 RC1 (7100) build in which the folder that is created as the root folder of the system drive (%SystemDrive%) is missing entries in its security descriptor. The company says that this problem can cause the following to occur: “applications that reference folders under the root may not install successfully or may not uninstall successfully. Additionally, operations or applications that reference these folders may fail. […] some specific operations, such as deleting the folder, will fail when they are performed from a non-elevated command prompt.”
Microsoft has released a hotfix for this problem, but it should only be applied to systems that are experiencing this specific problem. The fix is available through Windows Update.