jit.qt.grab problem

I'm trying to use the built in video camera on my MacBook Pro in Max5. I'm using the patches from this tutorial:https://cycling74.com/story/2009/10/26/153715/40

Anyway, I click the "open" message to jit.qt.grab and then turn on the [qmetro] and all is well for about 30 seconds. Then the internal video camera stops working and will not work again (in Max or any other program) until I restart the machine.

If I try to use the "open" message again, I get the error messages:
could not create video channel -9404
error opening device for grab

I have searched the forum but did not find a solution.

Any help would be appreciated,
Mitch