Can't Enable Filevault because Recovery Partition Missing
You will want to recreate the recovery partition following any of the answers here.


How to recreate Lion Recovery HD partition?
How can I create or recreate a Lion recovery partition?


That ensures the installer will throw an error if you have an issue with the partition map (or better it might fix that issue for you). Since FileVault 2 takes over the whole drive, you might also be out of luck to convert the drive with the other partitions present. Worst case, you could remove the partitions that aren't standard and run the conversion. Just like the BootCamp assistant cannot carve space out when FileVault is enabled, the graphical tools might not allow coexistence of non HFS+ partitions or volumes.