Are you attempting to force quit from the Activity Monitor or right-clicking the icon in the doc or how? I have found force quitting from the Activity Monitor is the best. If you can use the terminal you can also kill the program from there ... you can get the PID (Process ID) from the Activity Monitor and at the terminal prompt, type the command "kill -9 {PID}" ... {the PID is usually a 2-3 digit number representing the program running}.