>In general you don't want to try to copy the actual .MDF/.LDF files that represent your SQL Server database(s). If you try to do that you'll hit "file in use" errors such as you're seeing. Instead, use SQL Server's built-in backup function to create separate backup files, and then save those backup files someplace safe.

The reason for this behavior is the difference between SQL and VFP's database. A dbc contains relative paths to its tables. On SQL, however, everything is registered in the master database (i.e. master.mdb/ldb) with full absolute paths. And there seems to be some kind of back pointer, or key, whatever, in a database registered to it, which makes it "attached" (otherwise it is detached and then it may be moved to another SQL server). So I guess detaching means just dropping the related record from the master db and removing this backlink... pretty much like a dbf contains a reference to its .dbc somewhere in the header and there are records about it in the dbc, so it's a double link.

Once I was rebuilding my machine, reinstalling everything, and I almost managed to keep the master temp and other databases, with my mdb/ldbs as well. I kept the whole directory structure etc, and it almost worked, but it crashed because the path to SQL folders was slightly different, I think a different version number in the folder name. I could try to repeat everything (uninstall, force the folder name to the old one) but just ran out of patience.

The lesson I got from this is that SQL server's internal architecture is solid as long as you don't move the furniture. If you do, you may find yourself having to build a new house around the furniture.