无法创建抽象类或接口'DBSQLProvider的实例

Question

public abstract class ProviderBase
{
    static private ProviderBase instance = null;

    static public ProviderBase Instance
    {
          get
         {

            if (instance == null)
                instance = new DBSQLProvider();

            instance = (ProviderBase)Activator.CreateInstance(
            Type.GetType("DBSQLProvider"));

            Return instance
}