Attachments upload works - FileField upload does not

I've been trying to exercise the CCK file field provided by the FileField project

I have created a file field in a new content type and attempted to upload a file into an instance of the new content type.
After specifying the local file I press the upload button, the progress indicators run as if a file transfer is taking place and then stops (as if a transfer were complete). However - the interface does not change - i.e. there is no indication that a file has been transferred. I have inspected all relevant logs (Drupal, mySQL, PHP, Apache) and I see no evidence of a failure.

When I use the standard attachment upload facilities - this works fine.

Any hints on what might be going on and/or how to debug this problem is greatly appreciated.