Use this before your command line if your cards are with 2 or 3 gb:

setx GPU_FORCE_64BIT_PTR 0
setx GPU_MAX_HEAP_SIZE 100
setx GPU_USE_SYNC_OBJECTS 1
setx GPU_MAX_ALLOC_PERCENT 100
setx GPU_SINGLE_ALLOC_PERCENT 100
ethminer.exe --farm-recheck 200 -S xxxxxxx:xxxx -O x.x.xx.x.x.x -G --cl-local-work 256 --cl-global-work 16384