What does it mean when garageband says this disk is too slow?

When this error message appears, Garageband is trying to read or write audio tracks to the hard drive and cannot write or read the information fast enough. This can be caused by a very old Mac, a hard drive nearing its capacity, or a hard drive that is being used by another program at the same time. You will need to make sure that TimeMachine backup is disabled and any other applications or utilities that access the hard drive are not running when you run Garageband.