I currently have a successful implementation of the last Away3D source(4.x) using the Air SDK 23, but since the release of the Air SDK 24 and 25, I am unable to get Away3D to initialize at all. Does anyone have any suggestions?

Note: I am using stage3DManager and stage3DProxy too.

You do not provide any basic class/code to reproduce the problem… 
I run AIR and away3d without problems. So i’d say, start by checking your manifest.

make sure you have the correct version set
application xmlns=“http://ns.adobe.com/air/application/25.0”

and that your initial window has at least depthAndStencil to true and renderMode to direct.
Here an example that does work.

<initialWindow>
  <content>myApp.swf</content>
  <systemChrome>standard</systemChrome>
  <transparent>false</transparent>
  <visible>true</visible>
  <x>0</x>
  <y>0</y>
  <fullScreen>true</fullScreen>
  <requestedDisplayResolution>high</requestedDisplayResolution>
  <renderMode>direct</renderMode>
  <maximizable>true</maximizable>
  <minimizable>true</minimizable>
  <resizable>true</resizable>
  <depthAndStencil>true</depthAndStencil>
</initialWindow>

if it still not working, as said, provide a class to reproduce first. using view3D.

I’ve just transitioned my entire project to Air SDK 25 and had absolutely no issue. I’m don’t think your problem comes from the SDK itself…