public class Tools_
	{
		public Tools_(Label laberror)
		{
			this.laberror=laberror;
		}	
		private static ArrayList al = new ArrayList();
		private  Label laberror;	
		public  void checkvalidaty(RequiredFieldValidator val,Label lab,string error)
		{
		
			if (!val.IsValid)
			{
				lab.CssClass="error";
				al.Add(error);  
				laberror.Text=error;
				return;
				
			}
			else
			{
				lab.CssClass="td";
			}
			

		}
	}

Tools_ tls = new Tools_(Laberror);
			tls.checkvalidaty(valuserselected,Labuserselected,"Please choose value from the list!");