I have the same setup and Cuda works just fine. Check for other software that is causing a conflict, remove cuda and reinstall. Reboot... There is something causing a conflict. You might try rolling back one driver version.
To tell you the absolute truth I have used Ray-traced rendering exactly 2 times for professional work since it was introduced. There are lot's more efficient ways to achieve the same thing including the C4D integration, even with the LTE version that is included with AE.
I have the exact same setup and have encountered the same problem, any help would be greatly appreciated
Make sure you have installed the latest Cuda Driver, your OS is up to date, and that you have checked the box that says "Enable untested, unsupported GPU. . ." because the GPU in the new MacBook Pro R was introduced after it was decided to not continue down the Ray-traced rendering engine path and focus on integration with other 3-D Apps.