I am using the following to select have the dropdown list select an item from the list:
ddlIndustry.Items.FindByText(\"Trucking\").Selected = true;
Try using ClearSelection to clear previous selection:
ClearSelection
ddlIndustry.ClearSelection(); if (ddlIndustry.Items.FindByText("Cards") != null) ddlIndustry.Items.FindByText("Cards").Selected = true;