Value cannot be null. Parameter name: key

Doing something stupid here but cant figure it out, simple page with a grid on it pulling data from an object data source. Stored proc works and brings back columns I expect as listed in the markup

But get:

Value cannot be null.
Parameter name: key
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.ArgumentNullException: Value cannot be null.
Parameter name: key

Mark-up:

<telerik:RadAjaxManagerProxyID="RadAjaxManagerProxy2"runat="server">

<AjaxSettings>

<telerik:AjaxSettingAjaxControlID="RadGrid">

<UpdatedControls>

<telerik:AjaxUpdatedControlControlID="RadGrid"/>

</UpdatedControls>

</telerik:AjaxSetting>

</AjaxSettings>

</telerik:RadAjaxManagerProxy>

<telerik:RadGridID="RadGrid"AllowPaging="true"Skin="Bootstrap"ShowStatusBar="true"

PageSize="15"DataSourceID="ObjDSSubs"GridLines="None"AllowSorting="true"

AutoGenerateColumns="false"runat="server"AllowFilteringByColumn="true"

ShowFooter="True"ShowHeader="true" width="100%">

<clientsettingsallowkeyboardnavigation="false">

<SelectingAllowRowSelect="true"/>

</clientsettings>

<GroupingSettingsCaseSensitive="false"/>

<mastertableviewdatakeynames="Task_UUID">

<Columns>

<telerik:GridTemplateColumnUniqueName="Task_Title"AllowSorting="true"DataField="Task_Title"HeaderText="Task"ShowFilterIcon="false"AutoPostBackOnFilter="true"AllowFiltering="true">

<ItemTemplate><%#Eval("Task_Title")%></ItemTemplate>

</telerik:GridTemplateColumn>

<telerik:GridTemplateColumnUniqueName="Task_Details"AllowSorting="true"DataField="Task_Details"HeaderText="DEtails"AllowFiltering="false">

<ItemTemplate><%#Eval("Task_Details")%></ItemTemplate>

</telerik:GridTemplateColumn>

<telerik:GridTemplateColumnUniqueName="Task_Date"AllowSorting="true"DataField="Task_Date"HeaderText="Date" ShowFilterIcon="false"AutoPostBackOnFilter="true"AllowFiltering="true">

<ItemTemplate><%#Eval("Task_Date")%></ItemTemplate>

</telerik:GridTemplateColumn>

<telerik:GridTemplateColumnUniqueName="Task_Type"AllowSorting="true"DataField="Task_Type"HeaderText="Task_Type"ShowFilterIcon="false"AutoPostBackOnFilter="true"AllowFiltering="true">

<ItemTemplate><%#Eval("Task_Type")%></ItemTemplate>

</telerik:GridTemplateColumn

<telerik:GridTemplateColumnHeaderStyle-Width="15%"AllowFiltering="false">

<ItemTemplate>

<divclass="btn-group">

<ahref='/eupdate/edittask.aspx?id=<%#Eval("Task_UUID")%>' class='btn btn-sm btn-success'><iclass="glyphicon glyphicon-pencil"></i></a>

<adata-uuid='<%#Eval("Task_UUID")%>' title="Delete task" class='deletetask btn btn-sm btn-danger'><iclass="glyphicon glyphicon-remove"></i></a>

</div>

</ItemTemplate>

</telerik:GridTemplateColumn>

</Columns>

</mastertableview>

<pagerstylemode="NextPrev"AlwaysVisible="true"/>

</telerik:RadGrid>

<divclass="margin">

<asp:ButtonID="ButAdd"runat="server"Text="Add Task"cssclass="btn btn-sm btn-info"/>

</div>

<asp:ObjectDataSourceID="ObjDSSubs"runat="server"SelectMethod="Fetch"TypeName="cms.Tasks">

<SelectParameters>

<asp:ParameterName="Task_UUID"Type="string"DefaultValue=""/>

</SelectParameters>

</asp:ObjectDataSource>

Here's the Stack Trace

[ArgumentNullException: Value cannot be null.

Parameter name: key]

System.Collections.Generic.Dictionary`2.FindEntry(TKey key) +11702869

System.Collections.Generic.Dictionary`2.TryGetValue(TKey key, TValue& value) +13

Microsoft.VisualStudio.Web.PageInspector.Runtime.WebForms.SelectionMappingRenderTraceListener.GetLiteralTraceData(LiteralControl literal, TraceData& data) +97

Microsoft.VisualStudio.Web.PageInspector.Runtime.WebForms.SelectionMappingRenderTraceListener.GetTraceData(Object renderedObject) +421

Microsoft.VisualStudio.Web.PageInspector.Runtime.WebForms.SelectionMappingRenderTraceListener.EndRendering(TextWriter writer, Object renderedObject) +79

System.Web.UI.RenderTraceListenerList.EndRendering(TextWriter writer, Object renderedObject) +66

System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +170

System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +100

System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +25

System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +128

System.Web.UI.Control.RenderChildren(HtmlTextWriter writer) +13

System.Web.UI.WebControls.WebControl.RenderContents(HtmlTextWriter writer) +12

System.Web.UI.WebControls.WebControl.Render(HtmlTextWriter writer) +32

System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter) +66

System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter) +100

System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +25

System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children) +128

System.Web.UI.Control.RenderChildren(HtmlTextWriter writer) +13

System.Web.UI.WebControls.TableCell.RenderContents(HtmlTextWriter writer) +35