I would like to create a backup of my time machine backed volume on my external harddrive. I'm using, and would like to use, command line for some scripting purposes. Here is my command

sudo hdiutil create -ov -srcfolder /Volumes/Time\ Machine\ BU/ /Volumes/Additional\ Client\ Data/wolffeBackup.dmg

my Time machine backup is on one partition of my external harddrive. I want to create the disk image to the other partition. This is the error message I'm getting.

2009-06-23 15:19:47.079 copy-helper[1064:10b] bomCopierFileCopyError:/Volumes/Time Machine BU 1/Backups.backupdb/shizny’s MacBook Pro 15"/2009-06-23-151028/WolffeBrothers/.com.apple.timemachine.supported, error 1
2009-06-23 15:19:47.080 copy-helper[1064:10b] Error 1 (Operation not permitted) encountered copying "/Volumes/Time Machine BU/Volumes/Time Machine BU 1/Backups.backupdb/shizny’s MacBook Pro 15"/2009-06-23-151028/WolffeBrothers/.com.apple.timemachine.supported" (canceling)
could not access /Volumes/Time Machine BU 1/Backups.backupdb/shizny’s MacBook Pro 15"/2009-06-23-151028/WolffeBrothers/.com.apple.timemachine.supported - Operation not permitted

Anybody know why the disk image fails to be created?

Thanks in advance,