Com_Zimbra_Dnd not working with ZCS 6.0.1

[webman]

I recently upgraded a single-server installation from 5.0.16 to 6.0.1 on Ubuntu 6.06 (64bit). The upgrade went OK, but now the DnD attachment functionality is not working.

I've un-deployed and re-deployed the Zimlet on the server, re-started Mailboxd as well as as zmcontrol stop/start. I installed the 1.3.0 and 1.3.1 versions of the extension for Firefox 3.5.3, but still no luck. We use Mozilla Prism (a version shipped with a stable release of ZDesktop) as a front-end to our ZWC, and that is no longer working either.

There is no hint text beneath the subject box when composing, and dragging a file into that area has no effect.

Is there anything I can do to debug or provide more information, or does anyone know of a fix?

Thanks in advance