I probably should have left it alone, but last week, I needed to extract a .sit file, which I was told the default version of the OS X Stuffit Expander could not open, so I installed the free version of Stuffit. Since extracting that file, nothing will extract with StuffIt. Every archive I try tells me that it is an invalid archive, and to try again. I've attempted to uninstall Stuffit, but I don't know how to get the base OS X version back. Anyone have any insight into this issue?