Had the same problem here. For a workaround open a terminal and do the following:
gksu gedit /usr/bin/ubuntuone-preferences
find line 304 and change gtk.MODAL to gtk.DIALOG_MODAL
Save the file. Kill the hanging ubuntuone-prefererences process and restart. This time you will get a popup dialog with the error. Note that the dialog does not close if you click the close button; you have to close the popup from the window close button.
Had the same problem here. For a workaround open a terminal and do the following: ubuntuone- preferences
gksu gedit /usr/bin/
find line 304 and change gtk.MODAL to gtk.DIALOG_MODAL
Save the file. Kill the hanging ubuntuone- prefererences process and restart. This time you will get a popup dialog with the error. Note that the dialog does not close if you click the close button; you have to close the popup from the window close button.