unix files which will not open

I have just installed leopard on a g4PowerBook. Before I installed I copied all my files to a flash drive. When I opened the flash drive I found several, but not all, of the files had changed icons and would not open in Leopard. It is a horizon gray rectangle with exec (green) in the upper left corner. When I get info on the file it says it is a unix file. Has any had any luck in retrieving info from such a file? I doubt I am the only one in this position. Thanks