C# and Selenium

Most likely, the element isn't available in the DOM at the time Selenium searches for it. Since you're navigating through a login page, the page may still be loading or the element may be inside an iframe.

Wait for the element instead of searching immediately:
var wait = new WebDriverWait(driver, TimeSpan.FromSeconds(10));

var table = wait.Until(

SeleniumExtras.WaitHelpers.ExpectedConditions

.ElementIsVisible(By.Id("ctl00_MainContent_gvMyProviders_ctl00"))

);

There are multiple reasons it might not be working, such as;

• The element is inside an iframe

• The element isn't rendered yet

• Case sensitivity / whitespace

You can open DevTools → Console and run your querySelector or something else there to determine if it works.

Also in DevTools you can click the arrow/inspect icon then click the desired element on the page. It gets highlighted in the Elements panel, and you can right-click it → Copy → Copy XPath (or Copy selector for CSS, or Copy full XPath). If a selector works in the console but not your program then that confirms it's an iframe or timing problem, not a selector problem.