Disk too slow?

I'm running Mavericks 10.9.1 on my MacBook Pro Retina with 16Gb of DDR3 (1600) RAM and 758Gb flash-drive and the i7 processor running at 2.8 Ghz. There is 631Gb of free space on my SSD disk. GarageBand 6.0.5 keeps stopping during recording and telling me that my disk is too slow to record. I don't get it. This is the fastest MacBook I could buy only 2 months ago and already it's too slow to run one app all by itself. I tried turning off WiFi just in case some app was accessing the internet in the background without my knowledge. No change. No other apps are open or running. Went through the dock, one app at a time, making sure nothing else is running. My external drive is not connected so there's no automated backup in progress. Interface is the Saphire Focusrite 24Pro using Firewire 400. The interface runs flawlessly with any other apps and does playback from GarageBand without a hiccup, playing files much longer and with many more tracks than the one I am currently working on. This just started today. Never had an issue before now. Any ideas?