We are using Subversion to manage a big project.
Everyone normally has to lock a file before they can modify it.
There are several new new machines with Windows 7, SVN (64 bit) and this directive in the config file:
** = svn:needs-lock=true
*.* = svn:needs-lock=true*
If a user with one of these new machine creates a new file, the file will remain editable at all times even without requiring a lock. And when users update it without using a lock, it then causes a conflict.