time machine external drive dismounts

I have been using "My Book, Studio" from Western Digital for 4 years. Now suddenly when my machine goes to sleep or is shut down it cannot find the external drive (firewire connection).

Western Digital gave me a download of a "drive manager" but it still loses the drive and reports that the drive was dismounted improperly.

Any cure, or should I change the Energy Saver settings on the iMac. Help!

Please do not "hi-jack" someone else's thread. I moved your post here as a separate thread all its own.