Pixel Bender: Permissions problem when installing

I tried to install the extension "Pixel Bender" with Extension Manager, but, I received a message like this: "You do not have the appropriate permissions required to perform this operation. Contact your system Administrator to obtain permission". I do not understand this, because I am the admin of my computer, and I login as admin, my computer is Mac Pro with Snow Leopard 10.6.8, it's very sad to see so many issues when we are getting into a better technology, I download it off from Adobe Exchange, and follow all the instructions, now why I get into this block issue, I have been in so many forum and there is nothing posted to solve this conflict, can you let us to know what to do next in other to install these filters. Thanks for your prompt attention to this matter.

Guillermo Pimentel
gfpimentel@earthlink.net