XML sub hierarchy using classes

[Stu]

Hi,

Ive been using classes as output from webservices which until now have
worked well and have serialised into the xml i wanted.
Now i want to have a structure of
clients which have accounts which have securities

So ive defined the following classes (See below) when I look a the xml
when it gets to the <clientsaccounts> i dont see the full serialised
definition
Any ideas TIA

Stu
Public Class ClientDetails
Public ClientId As String = ""
Public clientInError As Boolean = False
Public clientAccounts() As ClientAccounts
End Class
<Serializable()> _
Public Class ClientAccounts
Public accountId As String = ""
Public accountnominal As Decimal = 0
Public ClientNominal As Decimal = 0
Public securities() As accountSecurity
End Class
<Serializable()> _
Public Class accountSecurity
Public securityId As String = ""
Public currency As String = ""
Public holdingInError As Boolean = False
End Class
<wsClientInfoResult>
<ClientDetails>
<ClientId>string</ClientId>
<clientInError>boolean</clientInError>
<clientAccounts>
<ClientAccounts xsi:nil="true" />
<ClientAccounts xsi:nil="true" />
</clientAccounts>
</ClientDetails>
</wsClientInfoResult>