If a file is access through two different instances of BC the file is not correctly locked and 2 users can open the file without getting any warning.
This can happen when the encrypted folder is on a network drive and the file accessed from 2 pcs or if 2 users on the same pc each have the encrypted folder mapped with different a different Drive letter and the pc is switched from one user to another with the first closing excel or logging out.
Not I have only tested this on windows 8.
Geoff