Here's more information. I tried making the conversion at the command line. No luck.
rob@MBP2:~ $ diskutil list
/dev/disk0
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *500.1 GB disk0
1: EFI 209.7 MB disk0s1
2: Apple_CoreStorage 499.2 GB disk0s2
3: Apple_Boot Recovery HD 650.0 MB disk0s3
/dev/disk1
#: TYPE NAME SIZE IDENTIFIER
0: Apple_HFS Macintosh HD *498.9 GB disk1
/dev/disk4
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *3.0 TB disk4
1: EFI 209.7 MB disk4s1
2: Apple_HFS TimeMachine3TB 3.0 TB disk4s2
rob@MBP2:~ $ diskutil cs convert /Volumes/TimeMachine3TB
Started CoreStorage operation on disk4s2 TimeMachine3TB
Resizing disk to fit Core Storage headers
Creating Core Storage Logical Volume Group
Attempting to unmount disk4s2
Switching disk4s2 to Core Storage
A problem occurred; undoing all changes
Undoing creation of Logical Volume Group
Reclaiming space formerly used by Core Storage metadata
Error: -69730: Unable to create boot loader partition due to the specifics of your partition map layout
rob@MBP2:~ $
http://www.youtube.com/watch?v=I568AnNzNdM