Hopefully, this will save some Rails programmers a bit of searching.

Permission denied – activesupport-2.3.2 or activesupport error when trying to run rake rails:freeze:gems?  For solution refer to http://www.ruby-forum.com/topic/184589 . 

In a nutshell, you need to edit line 28 of rubylibrubygems1.8gemsrails-2.3.2libtasksframework.rake to include sleep(5) between the Gem::GemRunner line and the mv line.