I cannot drag and drop audio files of any kind from Windows Explorer into Platinum. I think this was a problem before in another Sonar version. The Browser takes forever to finish scanning MIDI files. I have to sit there and wait every time I open it. The new Browser seems even slower for me. I was hoping that would have been improved in Platinum but it's still a turtle. I prefer Win Explorer to using the Browser.
 
I've tried dragging all types of files, wave, mp3, REX, etc. Nuttin'. Is this reproducible? Thanks!

If you are running Sonar as administrator (with admin privilages), this could happen. Windows' UAC (since Vista if I remember right) does not allow dragging and dropping stuff from low-privilage app to an app with high privilage (sorry if that didn't make much sense, I'm bad at explaining things). Try running Sonar without admin rights and see if that helps.
 
Alternatively, you can try and launch as administrator some other program (I personally recommend Reaper's browser, it works and caches things amazingly fast) as a wav browser. Note that Win Explorer can't be launched as administrator albeit there is a menu item that says the opposite. 
 
Hope that helps.

Just out of curiosity, why wouldn't you use Sonar's browswer (or is that the "new browser" you are referring to?)

I'm guessing the "new browser" is the Sonar's new browser. Since the in-browser search is recursive now, it's understandable that performance in some cases can be worse compared to X3/X2's browser (if, say, you've got a library with lots of subfolders).

AndreyB, you were absolutely correct! I've always been in the habit of stating Sonar with Admin Privileges. Never would have thought of that! And Dave, yeah, the Sonar Browser is very slow. I have all my loops, samples and MIDI files organized in one desktop folder. It's easier  to open that and pull what I need. I find myself always having to resize the Sonar Browser to accommodate the folder tree. Just dragging from the desktop folder is quicker for me.

if you're running sonar as admin, did you try running explorer as admin too?

OK, my experience hasn't been slow with Sonar's browser, but I don't think I've got the library of content you do.  Not sure how to help.  Is Sonar doing a conversion when you drag in the file (from either place)?  That will slow it down.  Not sure how to make that stop if it is happening.
 
Also, if you want to use the "window explorer" type of browsers, you can use import from the file menu and it functions like most other windows programs.  Not sure if that will be quicker for you or not.

pwalpwal
if you're running sonar as admin, did you try running explorer as admin too?

You can't run explorer as admin (well you can try, and it will even give you the "are you sure" prompt but it won't do anything). I beleive they have a huge conversation about this issue somewhere at MSDN forums (actually, it's done so to avoid exploits/viruses etc).
 
Southpaw, I can think of some choices for you... 
1. Disable UAC in Windows (not recommended for security reasons).
2. Don't run Sonar as admin (I think I remember only one situation when you would need to run Sonar as admin: when registering Dimension Pro for the first time... Or if you have several Z3ta+2 mods like Virus, but still there is a workaround for that case).
3. Search KVR forums for a standalone wavefiles' browser. There should be some free apps. For example, Foobar2000 can work as a decent mp3-wav-wma files browser (no .rex though), and it's got recursive search too, and it's way faster than Win Explorer.

AndreyB

pwalpwal
if you're running sonar as admin, did you try running explorer as admin too?

You can't run explorer as admin (well you can try, and it will even give you the "are you sure" prompt but it won't do anything).

thanks for the clarification, i just noticed this, and that the op has windows 8.1...

I just make Desktop one of the options from the drop-down menu in the Media Browser. Don't forget it's bi-directional, so you can drag files to and from the desktop.