Neuroharmony
I figured it out. This controller won't work with USB 3.0 ports, only 2.0. A workaround is to plug a USB 2.0 hub into a 3.0 port, which then converts the signal to 2.0.

That's a very useful tip, I marked the thread "solved" to attract attention to it.

Neuroharmony
It can't be that I've exceeded the number of devices allowed because the Oxygen works with the same setup. When I remove the Oxygen and plug in the Axiom, it isn't recognized.

Congratulations on diagnosing your problem and finding a workaround. I hope my previous advice did not lead you astray, as it clearly was not the source of your problem.
 
Your logic in the above statement, however, is incorrect. Suppose that the MIDI limit is 10 devices, and that you have plugged one or more prior MIDI devices into several USB sockets (remember that you failed to tell us what your machine is so who knows how many devices or USB sockets you have used). Each time you plug the Oxygen into a USB socket it counts as one device, and the combination of that device plugged into that particular socket is now MIDI port 10 in Windows count. Windows will let you plug that device into that port, and any ports it has previously occupied, as often as you like, because it is on the list of accepted devices/ports. But when you plug in the Axiom, that is a new device/port combination, now totalling 11 and above the limit. So the Axiom is not accepted, but the Radium still works and the problem is the device limit being exceeded. 

slartabartfast
Your logic in the above statement, however, is incorrect. Suppose that the MIDI limit is 10 devices, and that you have plugged one or more prior MIDI devices into several USB sockets (remember that you failed to tell us what your machine is so who knows how many devices or USB sockets you have used). Each time you plug the Oxygen into a USB socket it counts as one device, and the combination of that device plugged into that particular socket is now MIDI port 10 in Windows count. Windows will let you plug that device into that port, and any ports it has previously occupied, as often as you like, because it is on the list of accepted devices/ports. But when you plug in the Axiom, that is a new device/port combination, now totalling 11 and above the limit. So the Axiom is not accepted, but the Radium still works and the problem is the device limit being exceeded. 

 
Oh, OK. I didn't realize that the count was cumulative. I thought you meant the count of devices currently plugged in. Thanks for the clarification.

Zargg71
Is your pc up to date (win7 Sp1, with latest c++, etc)? If not you could try to update.
https://support.microsoft.com/en-us/kb/2977003 or use windows update.
Best of luck.

Yep, it's fully up to date. I'll go ahead and download the latest C++ anyway. Just to clarify, do I need the "C++ Redistributable Packages for Visual Studio 2013" ? And there are three files within it: vcredist_arm.exe, vcredist_x86.exe, and vcredist_x64.exe. Do I need all of them?

I would quit while you are ahead. Given this was a compatibility issue between a USB2 device and a USB3 port; there is no need look for trouble by updating parts of your machine which appear to be working.

scook
I would quit while you are ahead. Given this was a compatibility issue between a USB2 device and a USB3 port; there is no need look for trouble by updating parts of your machine which appear to be working.

This is a separate issue, see post #8. (Perhaps I should have started a new thread, but alas.)

Yes, adding unrelated issues in a thread makes problem solving difficult.
 
If you feel like winging it go ahead. A call to CW support would be the fastest most reliable way to solve runtime lib issues.

I should have quoted him in my answer. My bad

Zargg71
Is your pc up to date (win7 Sp1, with latest c++, etc)? If not you could try to update.
https://support.microsoft.com/en-us/kb/2977003 or use windows update.
Best of luck.

So I installed those files and still get the runtime error. Oh well, I guess it doesn't matter, and the solution is probably extremely obscure.
 
Thanks everyone.

I would as suggested, contact Cakewalk.
Best of luck.