the problem about BLE_DISC_STATE_CHAR

hi all,I am trying to write GattMessage from Central to Peripheral as soon as the connection is build. So i add the code in the location about  "BLE_DISC_STATE_CHAR",but i found  GATT_WriteLongCharValue here always return 0x16 (blePending).But if i add a few seconds ,the function here will return Success.I do not know why this can heppen.How can i send GattMsg fastly after the connection builded. Sorry my English is very poor,thanks everybody!