You might be right Geoff and it may be a sign of the external failing at this point.
The CF reader is a FW800 version and is coming off that external. It's the third in a chain of FW800 devices and I can't really plug the CF reader anywhere else without losing access to an external.
I'll look into getting a new external. Just thought it odd that this only happened after the update to Mountain Lion and thought I would check here.