Cant Load Old Worlds In Snapshot

I Cant Load My Old Worlds In The Snapshot Apparently.

I Cant Even Create A Backup Of The World And Load It

Its Very Annoying As I Have Most Of My Worlds In The Latest Release And I'm Playing A lot In The Snapshot. I Would Be Extremely Happy If You Fix This Glitch Or Email Me How To Fix It If It Isn't A Glitch. Thank You For Taking The Time To Read This. 

Henrikas