Nedan är ett alternativ, blir ju förstås en del kontroller.
'block 1
<asp:DropDownList ID="ddl1" Runat="server">
<asp:ListItem text="One"/>
<asp:ListItem text="Two"/>
<asp:ListItem text="Three"/>
<asp:ListItem text="Four"/>
</asp:DropDownList>
<asp:CompareValidator ID="Comparevalidator1" ControlToValidate="ddl1" ControlToCompare="ddl2" ErrorMessage="2" Operator="NotEqual" Runat="server"/>
<asp:CompareValidator ID="Comparevalidator2" ControlToValidate="ddl1" ControlToCompare="ddl3" ErrorMessage="3" Operator="NotEqual" Runat="server"/>
<asp:CompareValidator ID="Comparevalidator3" ControlToValidate="ddl1" ControlToCompare="ddl4" ErrorMessage="4" Operator="NotEqual" Runat="server"/>
<asp:CompareValidator ID="Comparevalidator4" ControlToValidate="ddl1" ControlToCompare="ddl5" ErrorMessage="5" Operator="NotEqual" Runat="server"/>
<asp:CompareValidator ID="Comparevalidator5" ControlToValidate="ddl1" ControlToCompare="ddl6" ErrorMessage="6" Operator="NotEqual" Runat="server"/>
'block2
<asp:DropDownList ID="ddl2" Runat="server">
<asp:ListItem text="One"/>
<asp:ListItem text="Two"/>
<asp:ListItem text="Three"/>
<asp:ListItem text="Four"/>
</asp:DropDownList>
<asp:CompareValidator ID="Comparevalidator6" ControlToValidate="ddl2" ControlToCompare="ddl1" ErrorMessage="1" Operator="NotEqual" Runat="server"/>
<asp:CompareValidator ID="Comparevalidator7" ControlToValidate="ddl2" ControlToCompare="ddl3" ErrorMessage="3" Operator="NotEqual" Runat="server"/>
<asp:CompareValidator ID="Comparevalidator8" ControlToValidate="ddl2" ControlToCompare="ddl4" ErrorMessage="4" Operator="NotEqual" Runat="server"/>
<asp:CompareValidator ID="Comparevalidator9" ControlToValidate="ddl2" ControlToCompare="ddl5" ErrorMessage="5" Operator="NotEqual" Runat="server"/>
<asp:CompareValidator ID="Comparevalidator10" ControlToValidate="ddl2" ControlToCompare="ddl6" ErrorMessage="6" Operator="NotEqual" Runat="server"/>
'sen ytterliggare 4 block