System.InvalidOperationException: session not created: This version of ChromeDriver only supports Chrome version x (SessionNotCreated)
There is a mismatch between the Chrome Browser installed and the chromedriver instance specified in the project. Update the chrome driver instance 'Selenium.Chrome.WebDriver' in the NuGet project manager to match the version of chrome installed on your operating system.
Element not found exception.
Dialogs in Dynamics applications are exposed as IFrames. An Iframe is a web page which is embedded in another web page or an HTML document embedded inside another HTML document.
Selenium expects to be told which context (IFrame) the current web driver is to perform the automation in. To achieve this we must switch between IFrame contexts when performing an action.
This can be achieved by directly accessing the web driver within the Dynamics Framework and specifying the ID of the iframe to switch to client.Browser.Driver.SwitchTo().Frame("frameid");. After the action is then performed the context must be reset client.Browser.Driver.SwitchTo().DefaultContent().
You can learn more about using IFrames in Selenium here.