I am using Time Machine with an external drive connected to a Macbook running Mountain Lion. I use backup encryption.
Whenever I connect the external drive TM asks for my password. The password I'm sure I used doesn't work, nor any others I've used in the past. However, it still backs up when I choose 'Backup now' and I appear to be able to use Time Machine to view old files in other backups!
Any ideas what may be causing this?