private static extern short SQLFreeHandle(short hType, IntPtr handle);

            SQLFreeHandle(SQL_HANDLE_DBC, hconn);

            SQLFreeHandle(SQL_HANDLE_ENV, henv);

            SQLFreeHandle(SQL_HANDLE_DBC, dbcHandle);                        

You must provide an Environment Handle provided by SQLAllocHandle as the first parameter. SQLAllocHandle is a replacement for SQLAllocEnv. When using SQLAllocHandle, you must call SQLSetEnvAttr and set the SQL_ATTR_ODBC_VERSION attribute to SQL_OV_ODBC3 before calling SQLDataSources. You must release Environment handle with SQLFreeHandle at the end.

        rc = SQLFreeHandle(SQL_HANDLE_ENV, sql_env_handle);

static extern short SQLFreeHandle(ushort HandleType, IntPtr InputHandle);

Declare Function SQLFreeHandle Lib "odbc32.dll" (ByVal HandleType As Short, ByVal InputHandle As IntPtr) As Short