How to prevent error: element is not currently intractable and may not be manipulated?

[Wel]

Using C# I was trying to replace a value from input box like this

        for (int second = 0; ; second++)
        {
            if (second >= 60) Assert.Fail("timeout");
            if (second > 15) break;

         Thread.Sleep(1000);
      }

        driver.FindElement(By.Id("input1")).Clear();
        driver.FindElement(By.Id("input1")).SendKeys(xxxx");

but I get error "element is not currently intractable and may not be manipulated" on the clear() line , why is that although I wait until page load ?