Find elements inside forms and iframe using Java and Selenium WebDriver
When using an iframe, you will first have to switch to the iframe, before selecting the elements of that iframe
You can do it using:
driver.switchTo().frame(driver.findElement(By.id("frameId")));//do your stuffdriver.switchTo().defaultContent();
In case if your frameId is dynamic, and you only have one iframe, you can use something like:
driver.switchTo().frame(driver.findElement(By.tagName("iframe")));