Sometimes you don't know that Forms Based Authentication is enabled on server and trying to access to the server and 440 Login Timeout error occurs. In this case check if FBA is enabled on server. Here is an example how to access to Exchange server when Forms Based Authentication is enabled on Exchange server. To access to an Exchange server with enabled FBA you have to execute method PerformFormsBasedAuthentication as first method after creation of "client" object. After that you can use any method from WebdavClient class.