Error freeing CUDA HS device memory (error: 999)

Hi,
I've found two tasks in my error list with this error message:
[05:32:13][6036][INFO ] CUDA global memory status (GPU setup complete):
------> Used in total: 1620 MB (396 MB free / 2016 MB total) -> Used by this application (assuming a single GPU task): 206 MB
[05:32:47][6036][INFO ] Checkpoint committed!
[05:33:48][6036][INFO ] Checkpoint committed!
[05:34:49][6036][INFO ] Checkpoint committed!
[05:35:49][6036][INFO ] Checkpoint committed!
[05:36:19][6036][ERROR] Error freeing CUDA HS device memory (error: 999)[05:36:19][6036][ERROR] Demodulation failed (error: 1010)!
05:36:19 (6036): called boinc_finish

I'm running 6 WUs samulteniously on GTX560 Ti with 2Gb so it may be the reason but I have never seen such error before.