When using TrueCrypt on your Mac you might want to backup or synchronize your TrueCrypt volumes to a non-Mac formatted (like NTFS ) external (USB) harddisk so you can view or edit the volumes under Linux  /Ubuntu or Windows.

By default, Mac OS X can only read NTFS formatted volumes, not write to it. To enable this, you have to install NTFS-3G for Mac OS X 2010.10.2

On some Mac OS X version (Lion in my case) you will additionally add a patch to prevent the following error message. This patch can be downloaded here