You need to set the permissions on database files if you manually move them to the databases folder on a mac server.
1. Right click the file (or files) and choose Get Info.
2. Expand the Sharing & Permissions section.
3. Hit the + button and add the FM Server User.
4. Change the Read Only permission to Read & Write
Now FM server will have the required permissions to open the files
Thanks Evan.. worked like a dream. I had (wrongly) assumed that by setting permission for 'Everyone' to R + W it would work... nope! Added FM Server... bingo!