ReSharper: Rename namespace not available?

Question

I'm trying to rename a namespace. For some reason, ReSharper isn't giving me the option to do so. I right click on it and choose Refactor, but everything except "Convert" is greyed out. I try the key combination CTRL R + R, and it says the command is unavailable. What am I doing wrong?

Here is documentation suggesting that what I am trying to do should work:

http://www.jetbrains.com/resharper/documentation/help20/Refactoring/renaming.html#renameNamespace

I'm using Visual Studio 2008 with R# 4.5