Portable version of GStreamer 1.5.2 on Windows

[Harry]

Trying : gst-launch-1.0 audiotestsrc num-buffers=500 ! avenc_ac3 ! avimux ! filesink
Result : ERROR: pipeline could not be constructed: no element "audiotestsrc".

This corresponds to my problem, where the failing line is constructing my first element :
  pvid->playbin = gst_element_factory_make("playbin", "playbin");

It seems like there is a problem with constructing elements.

More info of what I did:

I copied all the 284 DLLs in the 1.5.2 release to the same folder as are my executable and my DLL that calls GStreamer.
The folder structure is absolutely flat, with no sub-folders.
I can clearly see that libgstaudiotestsrc.dll is inside the folder.

Josh: According to what you said, this should work. Or am I missing something?