Download .unity3D file from server with WWW - zero length

Hi

We have an Unity iOS app that loads 3D models from a server.

Originally we were using the Mono WebClient - but that is causing issues with proxy servers.

I implemented a solution using TCPClient and NetworkStream - only to be informed that I needed the iOS Pro version. I merely have Unity Pro.

I then tried the WWW class - and that works fine for the likes of .png, .mp3 but .unity3d files come through with zero bytes.

There's no www.error - just zero length www.bytes.

It's not the file size to blame because bigger MP3 files have loaded successfully.

I tried swapping the content between two .mp3 and .unity3d files and the bogus .mp3 (with the model content) failed to load.

My question is: Is there some feature of the WWW class that actively bars the download of .unity3d files after inspecting their content?

Or else, how can I download .unity3d files with the WWW class?

Thanks in advance.