Help! After messing about with a .plist file, most applications fail to open. Starting at the beginning, basically I wanted to get iBooks Author running under 10.6.8 so yesterday, I followed the following step in a guide: From the Mac OS X desktop, hit Command+Shift+G and enter /System/Library/CoreServices/ Locate SystemVersion.plist and make a backup copy of it to the desktop Launch the Terminal and type the following: sudo nano /System/Library/CoreServices/SystemVersion.plist Locate the keys ProductUserVisibleVersion and ProductVersion and change their strings from 10.6.8″ to 10.7.2″ Hit Control+O to save the file It worked like a charm and I managed to install the app. I backtracked and changed the strings back to "10.6.8" and thought nothing of it. Today, my system tells me that it wants to update iTunes and Safari, which I agree to. However, afterwards both crash and fail to open. I check my system version in "About this Mac" and it shows 10.7.2. I go back into the .plist file and find that my changes haven't been made, so I go back through them and make sure I save. Now 10.6.8 shows up in "About This Mac". Now iTunes and Safari won't open which I figure is just a case of deleting the Lion versions and downloading older ones, but the problem is that now a lot of other applications such as iCal and even 3rd party apps like Spotify fail to open. I get the following error for both: "Spotify cannot be opened because of a problem. Check with the developer to make sure Spotify works with this version of Mac OSX. You may need to reinstall the application. Be sure to install any available updates for the application and OSX" Any suggestions?