How Do I Reactivate Backup Disk Encryption After Turning it Off?

Hey,

I'm running OS X 10.7.5 (Lion). I need to reactivate Backup Disk encryption after I turned it off.

In the last day or so Time Machine stopped asking for the Backup Disk password (p/w) to be entered after the Mac boots up. That is, the Backup Disk would initiate automatically. Which it has not done before. I searched Time Machine and Security options that might allow me to reinitiate that option. Can't find one.

The closest I came is a Apple Support page for Mountain Lion online that says when the Backup Disk is encrypted the Mac will ask for the p/w when the Mac is turned on. I figured if I turned Encryption off then on, I might have success.

I was able to turn Encryption off. I now can't see how to turn it on. Further, Time Machine now wants to Decrypt / De-Encrypt the disk. Argh!!

So I have removed the Backup Disk for now...

If anyone can help me solve both these issues, I'd be stoked!!

Many thanks,

Bryce