If you are connecting your Radium to your Mac via a USB3 port.. try using a powered USB2 hub between your Radium and your Mac...
Once that is done or if you are already using USB2 ports directly into your Mac then...
Do the following...
First, shut down your Mac and unplug your Radium49 (Don't just unplug the Radium!)
Then.....
1) Go to Applications/UTILITY via Finder
2) Run the Audio-Midi setup app
3) Go to the MIDI WINDOW (in the top menu bar)
4) CREATE A NEW MIDI DEVICE, call it whatever name you want...
5) Click GENERAL MIDI on
6) Install the drivers found here : http://m-audio.com/index.php?do=suppo...
(These are the 10.8.5 drivers. But they seem to work with Mavericks 10.9.4/5 for some people. )
7) Restart your Mac (Important step!)
8) Connect the keyboard
Failing that, the problem you have is the the Radium49 is no longer officially supported by M-Audio drivers in newer OS X versions later than Mountain Lion.... because it is now considered an "end of line' product by M-Audio, which means there will not be any new drivers released for it by M-Audio unfortunately.
You may find some additional help here....
http://community.m-audio.com/m-audio/topics/m_audio_keystation_with_osx_maverick s_9_1_doesnt_work_via_plug_n_play