There’s a bug in Codebook for OS X version 3.0.6 on OS X 10.8 Mountain Lion and 10.9 Mavericks, a newer API call we made causes the Main Window to lock up and fail to dismiss an initial feature highlight message. An update is on the way now, we are awaiting App Review approval now, which has been pretty quick lately in the Mac App Store (less than a day). If you need to work around this right now, get in touch directly and we can help.