Commission Regulation (EC) No 2050/1999 of 29 September 1999 amending Regulations (EC) No 1666/98, (EC) No 1667/98, (EC) No 1735/98, (EC) No 1758/98, (EC) No 1759/98, (EC) No 1760/98, (EC) No 2198/98, (EC) No 1066/1999, (EC) No 1067/1999, (EC) No 1392/1999, (EC) No 1393/1999, (EC) No 1704/1999 and (EC) No 1855/1999 opening standing invitations to tender for the export of cereals held by certain intervention agencies