Thank you for the post.
Please review the following Knowledge Base article KB 7616:
Ideally, to avoid damaging the file, the recommended method would be either to use FileMaker Server 12 as the file's host, or to install a copy of FileMaker Pro 12 to the dedicated host computer.
This way the only file being accessed resides on the server machine. No user should ever browse to the file to open, but instead should use the File > Open Remote… option, or a launcher file.
Using FileMaker Pro to open a file to share from a remote or network drive should be avoided if at all possible. The one host should open a local copy of the database to share.