Cycles render engine cuda problem

When I’m something big object or sean or BMW benchmark my GPU showing
1.CUDA error illegal address cuctxsynchroniz line 1372
2.CUDA error lunched failed.
my work is now stopped,
I’m using
GTX 980ti GPU 6gb vram
Core i3 processor
8gb ram
Windows 10.
But my another week GPU GTX 730 2gb vram is working properly,but it is too much slower.
How to fix this problem.