Just yesterday I turned on filevalut and my HD is 38GB and TM HD is 40GB when FV was off I use to be able to backup using TM know with it on and I have erased my volume that had TM it requires 60GB of space to backup why is that? This was not a problem when FV was off.
See this
http://att.macrumors.com/attachment.php?attachmentid=125417&stc=1&d=1216568063
See this
http://att.macrumors.com/attachment.php?attachmentid=125417&stc=1&d=1216568063