Files not syncronizing properly between systems

[djsdc]

We've had on multiple occasions now found out that some team members are not receiving updates correctly.  This has caused work to be lost and recreated as team members work on different versions of same file.   Has anyone else seen this issue?  Anyone know of a possible solution of workaround?

Note:
Each team member saves and closes their work before another begins.  We've made sure they are not updating the file at the same time.