When the connection between D3, the OpenDB Server and an ODBC compliant database is established, file handles are created in D3 and within the OpenDB server to manage file access to the relational database. If any of those file handles are invalidated by an interrupted communication to the RDBMS (for example, when table structures are changed while they are in use by OpenDB or when the RDBMS is restarted), the OpenDB server must to be restarted and the D3 ports that were accessing the RDBMS must be logged off and then back on again to reopen a valid handle.
See Restarting the OpenDB server for more information.