I've had this same issue in several instances. On the Mac, when you download any software from the internet, such as wordpress, when you unzip the download the system adds something like a resource fork to all the .php files so that when you open it it gives a system message that warns you that the file is a program/script and do you really want to open it.
It's a security feature, but the problem is, of course when I unzip the wordpress files in order to update the config file and upload to a webserver, WP does not work because apparently none of the PHP files are executable because of the warning my OS is putting on them. I know this must be a common problem so sorry if this has been discussed before, but what is the work around??