Native Error Numbers
For errors that occur in the data source (returned by SQL Server), the SQL Native Client ODBC driver returns the native error number returned to it by SQL Server. For errors detected by the driver, the SQL Native Client ODBC driver returns a native error number of 0. For more information about a list of native error numbers, see the error column of the sysmessages system table in the master database in SQL Server.
For errors returned by the Net-Library, the native error number is from the underlying network software.