When I try to open Brief Accounting I get an error "Data File is Locked"
This error means one of the following:
1. Another copy of the application has the data file open. Only one application can have the data file open at a time. Make sure the application is shutdown on the other machine.
2. There is an OS X permissions error on the data file or on the folder containing the file.
3. OS X didn't "release" the data file when the application was last shutdown. It still thinks the data file is open.
Try rebooting the computer where the data file resides. This will solve both #1 and #3. It usually solves the problem. If that doesn't work, try resetting the Permissions to Read & Write for all users on both the data file and the shared folder it is sitting in.