System UI has stopped

Hi,all

i9100g mokee rom 4.4.4
SYSTEM UI

if i 3 hours nothing with the mobile(deep sleep) if i locked the lockscreen then came
unfortunately the process com.android.systemui has stopped


logcat said
com.android.systemui has died

why?
i have :
Info:
memtotal: 792820 kb
memfree: 19296 kb
buffers: 9932 kb
cached: 171172 kb

its enough memfree or no?