Problems with illustrator cs4

I recently got an error message when trying to open illustrator cs4 saying the plugins for photoshop weren't working and it would cause the entire program to freeze and I would have to force quit.  From searching online it said to uninstall and delete, then to redownload and it should resolve the problem.  I did that, but I get an error message now when I try to reinstall.  It says error 2?  I have a mac and I need get this problem fixed asap