Filtering a GridView With Dropdowns

I am building an inventory dashboard to simplify having many different inventory reports. I have a gridview and four dropdown windows. I have it set to load the full query on page load, and then filter the list with the four dropdowns. The page loads great. But the first time I choose any dropdown, I get the message: "Maximum request length exceeded."

This is set in web.config:       <httpRuntime maxRequestLength="1000000" />

This query returns approximately 20,000 rows and actually runs fairly quickly. But filtering it down causes the above error.

This is my pageload event:

            VerifyRenderingInServerForm(form1);
            GridView1.GridLines = GridLines.Both;
            SqlInventory.FilterExpression = "[WAREHOUSE] LIKE '{0}' AND [BIN_LOCATION] LIKE '{1}' AND [PART_CODE] LIKE '{2}' AND [IC_LOT_NUMBER] LIKE '{3}'";
            GridView1.DataBind();

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My SQL datasource:

        <asp:SqlDataSource ID="SqlInventory" runat="server" 
            ConnectionString="<%$ ConnectionStrings:fin_pilotConnectionString %>" 
            SelectCommand="SELECT WAREHOUSE, BIN_LOCATION, PART_CODE, PART_DESC_1, IC_STATUS_CODE, IC_LOT_NUMBER, UNIT_OF_MEASURE, STANDARD_COST, IC_QTY_AVAILABLE, CURR_VALUE  FROM [VW_CURRENT_INVENTORY_ALL] ORDER BY [WAREHOUSE], [BIN_LOCATION], [PART_CODE]">
            <FilterParameters>
                <asp:ControlParameter ControlID="ddlWarehouse" Name="WAREHOUSE" PropertyName="SelectedValue" />
                <asp:ControlParameter ControlID="ddlBin" Name="BIN_LOCATION" PropertyName="SelectedValue" />
                <asp:ControlParameter ControlID="ddlPartCode" Name="PART_CODE" PropertyName="SelectedValue" />
                <asp:ControlParameter ControlID="ddlLotNbr" Name="IC_LOT_NUMBER" PropertyName="SelectedValue" />
                </FilterParameters>
        </asp:SqlDataSource>

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My dropdowns:

    <table style="width:800px; border:0">
    <tr>
        <td style="font-family:Arial narrow; font-size: small; width:50px">WHSE</td>
        <td style="font-family:Arial narrow; font-size: small; width:75px">BIN</td>
        <td style="font-family:Arial narrow; font-size: small; width:100px">PART</td>
        <td style="font-family:Arial narrow; font-size: small; width:215px">DESCRIPTION</td>
        <td style="font-family:Arial narrow; font-size: small; width:50px">STATUS</td>
        <td style="font-family:Arial narrow; font-size: small; width:100px">LOT NBR</td>
        <td style="font-family:Arial narrow; font-size: small; width:50px">UOM</td>
        <td style="font-family:Arial narrow; font-size: small; width:60px">STD COST</td>
        <td style="font-family:Arial narrow; font-size: small; width:50px">QTY</td>
        <td style="font-family:Arial narrow; font-size: small; width:50px">VALUE</td>
    </tr>
    <tr>
        <td>
            <asp:DropDownList ID="ddlWarehouse" runat="server" AutoPostBack="True" 
                DataSourceID="SqlWarehouse" DataTextField="WAREHOUSE" 
                DataValueField="WAREHOUSE" AppendDataBoundItems="True">
                <asp:ListItem Selected="True" Value="%">All Warehouses</asp:ListItem>
            </asp:DropDownList>
        </td>
        <td>
            <asp:DropDownList ID="ddlBin" runat="server" AutoPostBack="True" 
                DataSourceID="SqlBin" DataTextField="BIN_LOCATION" 
                DataValueField="BIN_LOCATION" AppendDataBoundItems="True">
                <asp:ListItem Selected="True" Value="%">All Bins</asp:ListItem>
            </asp:DropDownList>
        </td>
        <td>
            <asp:DropDownList ID="ddlPartCode" runat="server" AutoPostBack="True" 
                DataSourceID="sqlParts" DataTextField="PART_CODE" 
                DataValueField="PART_CODE" AppendDataBoundItems="True">
                <asp:ListItem Selected="True" Value="%">All Parts</asp:ListItem>
            </asp:DropDownList>
        </td>
        <td>&nbsp;</td>
        <td>&nbsp;</td>
        <td>
            <asp:DropDownList ID="ddlLotNbr" runat="server" AutoPostBack="True" 
                AppendDataBoundItems="True" DataSourceID="SqlLot" 
                DataTextField="IC_LOT_NUMBER" DataValueField="IC_LOT_NUMBER">
                <asp:ListItem Selected="True" Value="%">All Lot Numbers</asp:ListItem>
            </asp:DropDownList>
        </td>
        <td>&nbsp;</td>
        <td>&nbsp;</td>
        <td>&nbsp;</td>
        <td>&nbsp;</td>
    </tr>
    </table>

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And my Gridview:

        <asp:GridView ID="GridView1" runat="server" AllowSorting="True" CssClass="grid" AutoGenerateColumns="False" DataSourceID="SqlInventory" ShowHeader="false" Width="800px" >
            <Columns>
                <asp:BoundField DataField="WAREHOUSE" HeaderText="WHSE" SortExpression="WAREHOUSE" ShowHeader="False" >
                    <ItemStyle HorizontalAlign="Left" VerticalAlign="Top" Width="50px" Wrap="False" />
                </asp:BoundField>

                <asp:BoundField DataField="BIN_LOCATION" HeaderText="BIN" SortExpression="BIN_LOCATION"  >
                    <ItemStyle HorizontalAlign="Left" VerticalAlign="Top" Width="75px" Wrap="False" />
                </asp:BoundField>

                <asp:BoundField DataField="PART_CODE" HeaderText="PART_CODE" SortExpression="PART_CODE"  >
                    <ItemStyle HorizontalAlign="Left" VerticalAlign="Top" Width="100px" Wrap="False" />
                </asp:BoundField>

                <asp:BoundField DataField="PART_DESC_1" HeaderText="PART_DESC_1" SortExpression="PART_DESC_1" >
                    <ItemStyle HorizontalAlign="Left" VerticalAlign="Top" Width="215px" Wrap="False" />
                </asp:BoundField>

                <asp:BoundField DataField="IC_STATUS_CODE" HeaderText="STATUS" SortExpression="IC_STATUS_CODE"  >
                    <ItemStyle HorizontalAlign="Left" VerticalAlign="Top" Width="50px" Wrap="False" />
                </asp:BoundField>

                <asp:BoundField DataField="IC_LOT_NUMBER" HeaderText="LOT_NBR" SortExpression="IC_LOT_NUMBER"  >
                    <ItemStyle HorizontalAlign="Left" VerticalAlign="Top" Width="100px" Wrap="False" />
                </asp:BoundField>

                <asp:BoundField DataField="UNIT_OF_MEASURE" HeaderText="UOM" SortExpression="UNIT_OF_MEASURE"  >
                    <ItemStyle HorizontalAlign="Left" VerticalAlign="Top" Width="50px" Wrap="False" />
                </asp:BoundField>

                <asp:BoundField DataField="STANDARD_COST" HeaderText="STD_COST" SortExpression="STANDARD_COST"  >
                    <ItemStyle HorizontalAlign="Left" VerticalAlign="Top" Width="60px" Wrap="False" />
                </asp:BoundField>

                <asp:BoundField DataField="IC_QTY_AVAILABLE" HeaderText="QTY_AVL" SortExpression="IC_QTY_AVAILABLE"  >
                    <ItemStyle HorizontalAlign="Left" VerticalAlign="Top" Width="50px" Wrap="False" />
                </asp:BoundField>

                <asp:BoundField DataField="CURR_VALUE" HeaderText="CURR_VALUE" SortExpression="CURR_VALUE"  >
                    <ItemStyle HorizontalAlign="Left" VerticalAlign="Top" Width="50px" Wrap="False" />
                </asp:BoundField>
            </Columns>
        </asp:GridView>

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My goal is to load the entire inventory and then let the users filter it by any combination of the four dropdowns. How do I get around the error?