Help with this iterate problem
 

Good evening everyone.
What I am trying to simulate is a gear pump, but every time I iterate ,it comes the problem of 'Error: Update-Dynamic-Mesh failed. Negative cell volume detected.'
I have examined the grids in the gambit and checked it before iterating.But the problem always comes out after about 30 steps when I set the time step size of 0.0001s. Some authers suggest me to decrease the time step size. But if I decrease the time step size, the error comes out as well. I nearly tried everything that I can do, but still can't solve it. Can you help me and give some suggestions?
THANKS.