Error mounting: mount exited with exit code 1: helper failed with: mount: according to mtab, /dev/sdb1 is already mounted on / mount failed

Error mounting: mount exited with exit code 1: helper failed with:
mount: according to mtab, /dev/sdb1 is already mounted on /
mount failed

ProblemType: Bug
DistroRelease: Ubuntu 11.04
Package: gnome-disk-utility 2.32.1-0ubuntu4
ProcVersionSignature: Ubuntu 2.6.38-11.50-generic 2.6.38.8
Uname: Linux 2.6.38-11-generic i686
Architecture: i386
Date: Sat Oct 8 22:21:07 2011
ExecutablePath: /usr/bin/palimpsest
InstallationMedia: Ubuntu-Studio 11.04 "Natty Narwhal" - Release i386 (20110426.1)
ProcEnviron:
 LANGUAGE=es_MX:en
 LANG=es_MX.UTF-8
 SHELL=/bin/bash
SourcePackage: gnome-disk-utility
UpgradeStatus: No upgrade log present (probably fresh install)
XsessionErrors: (nautilus:1497): GdkPixbuf-CRITICAL **: gdk_pixbuf_format_get_name: assertion `format != NULL' failed