Rendertexture in Android crashes app

I have a camera generating a rendertexture which is then displayed with

 GUI.DrawTextureWithTexCoords(new Rect(8,-8, w, h), _rtCam.targetTexture as Texture, new Rect(sx, sy, tx, ty), false);

so that a selected portion of the render texture is actually shown. This approach works fine in stand alone deployments for Mac and Windows as well as in the web player. However, it fails in Android causing the app to crash on that line. The app was working just fine (as was the Graphics.DrawTexture alternative to GUI.DrawTextureWithTexCoords) when the app was deployed under an earlier version of Unity, 3.4 if I remember correctly.

I know there were some recent changes to ReadPixels and Apply, but I'm not using those directly. Are there any suggestions as how to remedy this issue?

-Thanks