It looks like Apple decided to include their own FTDI driver in Mavericks which will supersede the driver we've been using. The first time I tried to connect to my printer through Repetier-Host I actually got a kernel panic. I found this little gem which seems to take care of the issue by disabling OS X's internal FTDI driver. Mavericks does turn on the unknown publisher lock again by default so you'll either need to disable it, or after you attempt to run it and it fails it will show on the security tab that this software attempted to run and allow you to approve it.
Linky - http://www.enttec.com/support-center/kb/article/108-OS_X_Mavericks_(10.9)_-_IMPORTANT