Apple - Can't turn on FileVault after restore from Time Machine
FileVault 2 requirements
FileVault 2 requires OS X Lion and Recovery HD installed on your startup drive, which the OS X Lion installer will attempt to create at installation. If you receive an alert that no Recovery HD could be created and continued to install OS X Lion, you will be unable to use FileVault 2. See this article for more information. Please note that Recovery HD must be present on your computer's startup volume to use FileVault 2 (not an external Recovery HD).
Also, if you partitioned the new SSD yourself, ensure that you used the GUID partition table scheme.
Re-installing lion over the top of your existing install will recreate it for you.
I have described my solution in this blogpost: http://hints.binaryage.com/recover-lost-recovery-hd-for-filevault/