Application failed to Respond on Mac

When an application suddenly stops or fails to works properly, a common cause is corrupted preferences. Each application has its own preference files containing configuration data, and because they're read and written to so often these are rather susceptible to corruption.

Mac OS X may offer to reset its preferences. You can also do this manually.
Preference files, identified by the extension .plist, are stored in /Library/Preferences (on your main hard disk) and in /user/Library/Preferences, where user is your user account's home folder.

Having quit the application, make a folder on the Desktop called "Temp pref" and move all the app's preference files into this. Now relaunch the app. This forces it to rebuild its .plist file, which should solve the problem.

If it doesn't, just put the plists back. Some apps also have self-repair functions; for example, holding the Option key while launching may bring up a settings box.

Otherwise, you'll have to reinstall the application from its DVD or disc image file (.dmg).