using parameter markers in case in where clause of SelectCommand in SqlDataSource

Hello, I am trying to use a select command in a SqlDataSource to load a GridView. I am trying to use parameter markers in a case in the where clause of the select but get the following error when the sql executes...

Message: Sys.WebForms.PageRequestManagerServerErrorException: SQL0417: Combination of parameter markers not valid.
Cause . . . . . : The statement string specified as the object of a PREPARE statement contains a predicate or expression where parameter markers have been used as operands of the same operator. The following restrictions apply to the use of parameter markers: -- Both the operands in a predicate cannot be parameter markers. For example, specifying predicates of the form: ? = ? or ? = ( SELECT ? FROM x ) are not valid. -- Both the operands in a expression cannot be parameter markers. For example, specifying an expression of the form: ? + ? is not valid. -- At least one of the operands in the BETWEEN predicate cannot be a parameter marker. For example, specifying the predicate of the form: ? BETWEEN ? and ? is not valid. -- At least, one of the operands of the IN predicate must not be a parameter marker. For example, specifying the predicate of the form: ? IN (?, ?, ?) is not valid. Recovery . . . : Correct the statement so that all operands of the predicate or expression are not parameter markers. A CAST specification can be used in most cases to assign attributes to a parameter marker. Try the request again.
Line: 869
Char: 13
Code: 0

...and i've tried assigning a type to the parameters without success...and I'm not sure how the errror is advising me to use cast?

The code for my GridView and SqlDataSource is as below...

    <div id="Div1" style="position: absolute; left:900px; top:50px; height:350px; width:650px;
     font-family: Arial; font-size: 15px; color:black; overflow:auto">
        <asp:GridView ID="listserviceorders" runat="server"
            AllowSorting="True" AutoGenerateColumns="False"
            DataSourceID="SqlDataSource3" AllowPaging="False"
              HeaderStyle-Wrap="True"
             GridLines="None" Visible="true"
              Caption='<table class="Freezing" ><tr><td>Service Orders List</td></tr></table>'
              CaptionAlign="Left" SelectedRowStyle-BackColor="#CCFFCC"
               OnSelectedIndexChanged="showserviceorders" >
            <AlternatingRowStyle BackColor="#CCCCFF" Wrap="False" />
            <Columns>
                <asp:CommandField ShowSelectButton="True" ButtonType="Image" SelectImageUrl="linkimage.gif" />
                <asp:BoundField DataField="sosono" HeaderText="SO Number"
                    SortExpression="sosono" />
                <asp:BoundField DataField="sosadn" HeaderText="Street Number"
                    SortExpression="sosadn" />
                <asp:BoundField DataField="sosadd" HeaderText="Address"
                    SortExpression="sosadd" />
                <asp:BoundField DataField="sordte" HeaderText="Request Date"
                    SortExpression="sordte" />
                <asp:BoundField DataField="sortdt" HeaderText="Returned Date"
                    SortExpression="sortdt" />

            </Columns>
            <HeaderStyle CssClass="Freezing" />
        </asp:GridView>

        <asp:SqlDataSource ID="SqlDataSource3" runat="server"
            ConnectionString="<%$ ConnectionStrings:startpagegridview1ConnectionString %>"
            ProviderName="<%$ ConnectionStrings:startpagegridview1ConnectionString.ProviderName %>"



            SelectCommand="Select t1.sosono, t1.sosadn, t1.sosadd, case when t1.sortdt='01/01/0001' then NULL else t1.sortdt end as sortdt, case when t1.sordte='01/01/0001' then NULL else t1.sordte end as sordte from bllib400.blpso t1 where soddte='01/01/0001' and socode=? and sordte=? and sortdt= case when ? is null then '01/01/0001' else ? end">
            <SelectParameters>
                <asp:ControlParameter ControlID="sobydate2GridView1" Name="?"
                    PropertyName="SelectedDataKey.Values(SOCODE)" />
                <asp:ControlParameter ControlID="sobydate2GridView1" Name="?"
                    PropertyName="SelectedDataKey.Values(SORDTE)" />
                <asp:ControlParameter ControlID="sobydate2GridView1" Name="?"
                    PropertyName="SelectedDataKey.Values(SORTDT)"/>
                <asp:ControlParameter ControlID="sobydate2GridView1" Name="?"
                    PropertyName="SelectedDataKey.Values(SORTDT)"/>
            </SelectParameters>
        </asp:SqlDataSource>

</div>

...My intent in the where clause being that when the SORTDT parameter comes from the "parent" control as NULL it is replace in the select with '01/01/0001'.

Could someone kindly show me how to use the parameter markers correctly in the case?

Any help greatly appreciated,

Roscoe

Re: using parameter markers in case in where clause of SelectCommand in SqlDataSource

Hello

In the standard SqlDataSourceI don't think it's suitable for you to use "?"question markas a parameter tokenI mean you should use @parameterName insteadAnd your @parameterName should be the same defined in the SelectParameters

Reguards