UDO / Date Type field ..

Having problems with UDO and a screen I've designed .. I have two dates in my UDO which i have bound to the display .. I attempt to prefill the dates with the following code ..

form.DataSources.DBDatasources.Item("@MyTest").SetValue("U_StartDate",0, GenApp.DefaultStartDate.ToString());

form.DataSources.DBDataSources.Item("@MyTest").SetValue("U_EndDate",0,
GenApp.DefaultEndDate.ToString());

....

form.Update();

My GenApp is a static class contains the methods DefaultStartDate, DefaultEndDate which returns

DateTime values ..

The dates don't display in the screen , though the static class does return values .. Any one have any suggestions ?

Thanks