need help on error message from gridview update

[Jon Paal]

why am I getting this error ? ID field is identity, type int


Error message on update
============================
Incorrect syntax near 'nvarchar'.
Must declare the scalar variable "@id".


Datasource
==================
<asp:SqlDataSource ID="SqlDataSource1" runat="server"
....
UpdateCommand= "UPDATE [Properties] SET [PropertyName] = @PropertyName WHERE id = @id" >
<UpdateParameters>
<asparameter Name="ID" Type="Int32"/>
<asparameter Name="PropertyName" Type="String"/>
</UpdateParameters>
...

Gridview
================
<asp:GridView ID="GridView1" runat="server"
AutoGenerateColumns="False"
DataSourceID="SqlDataSource1"
DataKeyNames="id"
....>