Problem mounting a USB flashdrive on Intrepid

[Steven Davies-Morris]

It mounts and is both read/writeable on my computer (Intrepid). But
not on the new Intrepid box I just put together last week for my wife.
The device shows up/disappears when I plug it in/remove it. But when
accessed her user is told:

Cannot mount volume
You are not privileged to mount this volume

And then about 30 seconds later she gets:

Unable to mount 2.0 GB media
Dbus error org.freedesktop.DBus.Error.NoReply.
Did not receive a replay. Possible causes include: the remote
application did not send a reply, the message bus security policy
blocked the reply, the reply timeout expired, or the network
connection was broken.

The device in question is an Emprex 2.0 GB. sfdisk -l reports that it
is a FAT16 file system.

This is probably glaringly obvious, but I'm drawing a complete blank
right now. Point me to the sky, please.
-- 
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NP: nothing