Why Can't I Build in Unity 4.5.3f3 and Unity 4.6?

When building for PC on Windows 7x64, I get the following error:

Moving file failed

Moving Temp/StagingArea/Data to Temp/StagingArea/testBuild_Data

Try Again - Force Quit - Cancel

... And then in the console...

Error building Player: IOException: Failed to Move File / Directory from 'Temp/StagingArea/Data' to 'Temp/StagingArea/testBuild_Data'

... And the build fails

What I've tried:

• Using a completely new, empty project

• Running as administrator

• Uninstalling antivirus

• Moving project out of Dropbox

• Removing "read-only" from project and Unity install folders

• Disabling Windows folder indexing on the project folder

Note that building for the web player works fine, and building for Android has the identical problem. I can work around this problem for PC by going to the staging area and running the build from there, but not such luck for Android. I have

Can anyone help me to solve this?