Error:

The remote name could not be resolved: 'portal'
at System.Net.HttpWebRequest.GetResponse() at Microsoft.SharePoint.Client.Idcrl.SharePointOnlineAuthenticationProvider.GetIdcrlHeader(Uri url, Boolean alwaysThrowOnFailure, EventHandler`1 executingWebRequest) at Microsoft.SharePoint.Client.Idcrl.SharePointOnlineAuthenticationProvider.GetAuthenticationCookie(Uri url, String username, SecureString password, Boolean alwaysThrowOnFailure, EventHandler`1 executingWebRequest) at Microsoft.SharePoint.Client.SharePointOnlineCredentials.GetAuthenticationCookie(Uri url, Boolean refresh, Boolean alwaysThrowOnFailure) at Microsoft.SharePoint.Client.ClientRuntimeContext.SetupRequestCredential(ClientRuntimeContext context, HttpWebRequest request) at Microsoft.SharePoint.Client.SPWebRequestExecutor.GetRequestStream() at Microsoft.SharePoint.Client.ClientContext.GetWebRequestExecutor() at Microsoft.SharePoint.Client.ClientContext.GetFormDigestInfoPrivate() at Microsoft.SharePoint.Client.ClientContext.EnsureFormDigest() at Microsoft.SharePoint.Client.ClientContext.ExecuteQuery() at EducateSpbRu.XXXHandler.EnumerateSPSList(String siteRoot, String docLibRootUrl, String docLibName, String camlQuery) at EducateSpbRu.XXXHandler.ProcessRequest(HttpContext context)