Thanks for the suggestion, but since all worked fine in the past, I'd like to continue using this kind of connection.
I don't know if DBD::ODBC would rely on sockets to access a remote Windows computer over the network (intranet/internet). In that case I might have the same problem.
But as a last resort I might try what you suggest, or use the php client that instead works fine on the same computer connectiong to the same remote server.