one thing that you can apply to solve your issue ,
if you pass where clause parameters at last then your query execute perfactly
as in this
Dim query As String = "UPDATE PRODUCT SET ORDER_NO = :od WHERE PACKING = :pn"
Dim command As OracleCommand = New OracleCommand(query, code.OCon) _
With {.CommandType = CommandType.Text, .BindByName = True}
command.Parameters.Add("pn", OracleDbType.Varchar2).Value = packingnumber
command.Parameters.Add("od", OracleDbType.Varchar2).Value = ordernum
Make this
Dim query As String = "UPDATE PRODUCT SET ORDER_NO = :od WHERE PACKING = :pn"
Dim command As OracleCommand = New OracleCommand(query, code.OCon) _
With {.CommandType = CommandType.Text, .BindByName = True}
command.Parameters.Add(":od", OracleDbType.Varchar2).Value = ordernum
command.Parameters.Add(":pn", OracleDbType.Varchar2).Value = packingnumber
Then it's work 100% , please try