StimTracker connectivity

I have been having a problem where I run a StimTracker off of a USB once, but when I unplug it and try to plug it in again or the computer falls asleep, I get errors finding the StimTracker again. The port is active and the FTDI driver is running. I am running a Mac, El Capitan with SuperLab 5.5.
I may be able to switch ports once, but once that port is running it gives me the same error message. It does not always clear when I reboot the machine. Any thoughts?

The messages are as follows
13:35:29: Serial port has not been specified. Please select a serial port.
13:35:29: SuperLab was unable to initialize the serial port for the Serial Output event.

It’s hard to tell what’s going on exactly. Have you updated the USB driver? The Mac one was updated just three weeks ago.