OK, if you don't have a sudden motion sensor, you should take out that bit of the sentence in the error message and read the rest, because that is what is happening: you are overloading your Mac with your Logic project. And believe me, it is not too hard to overload ANY Mac using Logic, you need to know what uses lots of CPU and what doesn't.
1. Having an SI track selected during playback. Puts the SI in "Live mode" which is much more CPU intensive. Have an audio or aux track selected instead.
2. Any flexing or other realtime pitch alteration to audio is CPU-intensive. Use Freeze, or Bounce-in-place when done
3. Some synths use a LOT of CPU, very much depending on the patch. Reverbs (Space designer) are CPU hungry, as are multiband compressors. Don't forget many 3rd party synths/samplers have their own effect section, using the synths built-in effects can make a synth patch much heavier on the CPU too.
Also, a system disk that is too full (less than ± 25 % of its' capacity free) can tax the CPU, as the "dumping to disk & retrieving from disk" of RAM content becomes harder for the system.
4. Also, if you use the system disk as audio file/recording disk, you're doubly taxing it (RAM writes and reads to that same disk - that is why a separate disk for recording is recommended, to avoid "traffic" on the system disk). You should Freeze Instrument tracks that need lots of CPU, that makes a difference too.
5. And don't forget the buffer settings: set it to 512 or 1024 when playing back, and set the process buffer range to Large.
6. Also, when audio recoring is done, set all audiotracks to No Input.
Freezing:
http://documentation.apple.com/en/logicpro/usermanual/index.html#chapter=9%26sec tion=16%26tasks=true