ASP.Net Error Cannot have multiple items selected in a DropDownList

If you are getting exception like "Cannot have multiple items selected in a DropDownList", its most probable cause is you are using below line in your application

ddlItems.FindByValue("data").Selected = true;

To handle this error, you need to clear the previous selection of your drop down as following:

ddlItems.ClearSelection();
ddlItems.FindByValue("data").Selected = true;

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