可以尝试的两件事

1. 在以下两行之间输入断点.并查看第二行时您在哪个页面上

2. 通过Thread.Sleep在这两行之间引入一点延迟

1. put the break point between the following two lines. And see which page are you in when the second line is hit

2. Introduce a slight delay between these two lines via Thread.Sleep

Driver.FindElement(By.Id("submenuitem4")).Click(); var headerelement = Driver.FindElement(By.ClassName("header"));

Driver.FindElement(By.Id("submenuitem4")).Click(); var headerelement = Driver.FindElement(By.ClassName("header"));