web.config setting for webservices, cascading dropdownlist

hi,friend's 
I have a 1 Lac records in table ITMMST  and i am using dropdownList inside emptydataTemplate which is bind through CascadingDropDown  and webservice as per below
code, when Dropdownist  is bind with few hundered records it works but when it fill with all 1 lac recodrs it gives [Method error].so, Why is it so?
Is there limit of CascadingDropDown of ajaxcontroltoolkit or any other Problem or any web.config setting for web services for large data required ? how can i Solved it ?
please help me?

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<asp:DropDownList ID="DDitemnameins" runat="server" Width="80px">
</asp:DropDownList>
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