Time machine backup encryption error

Hello,

I have recently enabled FireVault2 on my MacBook Pro (10.8.5) so that I can encrypt my files.

I would also like to enable encryption on my Time Machine back up drive.

However, when I set up the encryption process, I get an error message.

This is the error message I am receiving:

There was an error preparing the Time Machine backup disk “Time Machine Backups”.

A Recovery System for the targeted disk is required.

I don't know where to go from here so any suggestions would be helpful!

Thanks so much,

Jennifer