Login into magento problem

[sokolman]

Hello,
I have probem with URL when using client.AuthenticateAdmin(...).
System.ArgumentOutOfRangeException
StartIndex cannot be less than zero.
Parameter name: startIndex
at System.Net.WebClient.OpenRead(Uri address)
at Magento.RestApi.MagentoApi.Login(MagentoWebClient webClient, String loginUrl, String userName, String password, String oauthToken)