Installer Crashed

I tried to install Edgy in a Virtual Machine with VMware Server.

The host OS is Ubuntu Dapper with a custom kernel 2.6.17.7.

Here is the message I get during install :
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Traceback (most recent call last):
  File "/usr/bin/ubiquity", line 132, in ?
    install(sys.argv[1])
  File "/usr/bin/ubiquity", line 57, in install
    ret = wizard.run()
  File "/usr/lib/ubiquity/ubiquity/frontend/gtkui.py", line 264, in run
    self.progress_loop()
  File "/usr/lib/ubiquity/ubiquity/frontend/gtkui.py", line 545, in progress_loop
    raise RuntimeError, ("Install failed with exit code %s\n%s" %
RuntimeError: Install failed with exit code 1
Traceback (most recent call last):
  File "/usr/share/ubiquity/install.py", line 1284, in ?
    install.run()
  File "/usr/share/ubiquity/install.py", line 307, in run
    self.umount_source()
  File "/usr/share/ubiquity/install.py", line 575, in umount_source
    raise InstallStepError("Failed to unmount source device")
InstallStepError: <unprintable instance object>