who know the reason of "the launch timed out and was terminated"

I have two GTX295 cards.
I ran the cufft in a “for” loop.
The cufft appears very unstable, and sometime report “CUFFT_EXEC_FAILED”
I used getlastcudaerror(), it returned “the launch timed out and was terminated”. who know what’s the meaning of it?

Thank you very much.

nobody know?