Resetting the ports on my MacBook eliminated all of my midi issues that started after upgrading to OS X Mavericks.
Try the following steps:
1. Shut down
2. Hold down the following keys simultaneously for 30 seconds and then let go:
shift
control
option
the power button
(You will not see or hear anything)
3. Press and release the power button to start the MacBook, and quickly press and hold the following keys until the mac plays a tone:
option
command
the letter p
the letter r
(The mac will play the same tone a few times and then continue booting)
In addition to these steps, I found that turning on my midi devices BEFORE plugging them into the mac was important.