A couple of other people are reporting problems with detecting devices on MacBooks, so it looks like it is an issue with libusb. Here is a build with a different version of libusb (libusbx 1.0.12), see if that fixes it:
If it doesn't then I will revert to the old method for detecting devices on OS X for the next release. That will mean that there will be no support for MTP based devices on OSX, but, I don't see any other solution.
A couple of other people are reporting problems with detecting devices on MacBooks, so it looks like it is an issue with libusb. Here is a build with a different version of libusb (libusbx 1.0.12), see if that fixes it:
http:// calibre- ebook.com/ downloads/ betas/calibre- 0.8.67. dmg
If it doesn't then I will revert to the old method for detecting devices on OS X for the next release. That will mean that there will be no support for MTP based devices on OSX, but, I don't see any other solution.