Can you post your configuration and type of card?
setx GPU_MAX_ALLOC_PERCENT 100
setx GPU_USE_SYNC_OBJECTS 1
sgminer.exe --kernel darkcoin -o stratum+tcp://hiro.suprnova.cc:3313 -u jdebunt.1 -p x --thread-concurrency 8192 -I 13 -g 2 -w 256 --lookup-gap 2 --no-submit-stale --auto-fan --temp-target 74,72
Card 1 : Asus Radeon 280x
Card 2 : Sapphire Radeon 7970
That looks fine, try specifying the number of shaders for each card.
The 7970 being 2048 and the 280X 1536. Also delete the .bin files in the sgminer folder before mining again.