soap xsi:nil="true" problem for multi level objects

[emil]

Hello;
i try to do object serialization xml with using soap.But it shows me just
till 4th level.
After 3th level xsi:nil="true" appears.there is the xml instance;

<soap:Body>
<OTA_VehAvailRateRQ xmlns="http://tempuri.org/">
<POS>
<source>
<RequestorID>
<CompanyName xsi:nil="true" />
<ID>string</ID>
<ID_Context>string</ID_Context>
<Instance>string</Instance>
<Type>string</Type>
<URL>string</URL>
<MessagePassword>string</MessagePassword>
</RequestorID>
</source>
</POS>

Does anybody know the solution?My another question is for complex(multi level)
objects i couldnt get any neither get nor post xml.How to accomplish that?

i ll appreciate if You help me.
Thanks for help