2018/5/9追記

日本時間の2018/5/9より配信されたKB4103721でこの問題は修正されました

Windows 10 RS4(Spring Upate)のInsider Previewが配信されていますが、これをインストールするとWindows Server 2016 EssentialsのClient Connectorがインストールできなくなる場合があります。

Logには、以下のように表示されています。

[2888] 180331.170510.1203: ClientSetup: Start of ClientDeploy
[2888] 180331.170510.2200: General: Initializing...C:\Program Files\Windows Server\Bin\ClientDeploy.exe
[2888] 180331.170510.2280: ClientSetup: Create client deployment registry subkey if necessary
[2888] 180331.170510.2350: ClientSetup: The initial launching way: -LaunchedFrom:installer
[2888] 180331.170510.2359: ClientSetup: The initial state is set
[2888] 180331.170510.2359: ClientSetup: The initial serverName: 192.168.11.20
[2888] 180331.170510.2359: ClientSetup: Loading Wizard Data
[2888] 180331.170510.2420: ClientSetup: Saving Wizard Data
[2888] 180331.170510.2459: ClientSetup: Current DeploymentStatus=Start
[2888] 180331.170511.1834: ClientSetup: Showing the Client Deployment Wizard
[2888] 180331.170511.6532: ClientSetup: The input server name is 192.168.11.20
[9936] 180331.170511.6616: ClientSetup: Entering ConnectorWizardForm.RunTasks
[9936] 180331.170511.6621: ClientSetup: Running Task with Id=ClientDeploy.PreConfiguration
[9936] 180331.170511.6691: ClientSetup: The configuration cab will be downloaded from 192.168.11.20
[9936] 180331.170511.6741: ClientSetup: Download file Setup.cab from server
[2888] 180331.170511.6830: ClientSetup: InitWizard, The currrent stage is ConnectingToServer
[2888] 180331.170511.6840: ClientSetup: Set the Deployment Sync Event
[9936] 180331.170511.6870: ClientSetup: Making web request: https://192.168.11.20//connect/default.aspx?Get=Setup.cab&LanguageId=1041&64bit=1
[9936] 180331.170511.7588: ClientSetup: Failed to download Setup.cab from server: System.Net.WebException: 接続が切断されました: SSL/TLS のセキュリティで保護されているチャネルに対する信頼関係を確立できませんでした。 ---> System.Security.Authentication.AuthenticationException: 検証プロシージャによると、リモート証明書は無効です。
   場所 System.Net.Security.SslState.StartSendAuthResetSignal(ProtocolToken message, AsyncProtocolRequest asyncRequest, Exception exception)
   場所 System.Net.Security.SslState.CheckCompletionBeforeNextReceive(ProtocolToken message, AsyncProtocolRequest asyncRequest)
   場所 System.Net.Security.SslState.ProcessReceivedBlob(Byte[] buffer, Int32 count, AsyncProtocolRequest asyncRequest)
   場所 System.Net.Security.SslState.StartReceiveBlob(Byte[] buffer, AsyncProtocolRequest asyncRequest)
   場所 System.Net.Security.SslState.CheckCompletionBeforeNextReceive(ProtocolToken message, AsyncProtocolRequest asyncRequest)
   場所 System.Net.Security.SslState.ProcessReceivedBlob(Byte[] buffer, Int32 count, AsyncProtocolRequest asyncRequest)
   場所 System.Net.Security.SslState.StartReceiveBlob(Byte[] buffer, AsyncProtocolRequest asyncRequest)
   場所 System.Net.Security.SslState.CheckCompletionBeforeNextReceive(ProtocolToken message, AsyncProtocolRequest asyncRequest)
   場所 System.Net.Security.SslState.ProcessReceivedBlob(Byte[] buffer, Int32 count, AsyncProtocolRequest asyncRequest)
   場所 System.Net.Security.SslState.StartReceiveBlob(Byte[] buffer, AsyncProtocolRequest asyncRequest)
   場所 System.Net.Security.SslState.CheckCompletionBeforeNextReceive(ProtocolToken message, AsyncProtocolRequest asyncRequest)
   場所 System.Net.Security.SslState.ForceAuthentication(Boolean receiveFirst, Byte[] buffer, AsyncProtocolRequest asyncRequest)
   場所 System.Net.Security.SslState.ProcessAuthentication(LazyAsyncResult lazyResult)
   場所 System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   場所 System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   場所 System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
   場所 System.Net.TlsStream.ProcessAuthentication(LazyAsyncResult result)
   場所 System.Net.TlsStream.Write(Byte[] buffer, Int32 offset, Int32 size)
   場所 System.Net.ConnectStream.WriteHeaders(Boolean async)
   --- 内部例外スタック トレースの終わり ---
   場所 System.Net.HttpWebRequest.GetResponse()
   場所 Microsoft.WindowsServerSolutions.ClientSetup.CSCommon.DownloadFileFromConnectSite(String outputDirectory, Uri serverUrl, String fileName, Int32 languageId, Boolean is64bit)
[9936] 180331.170511.7598: ClientSetup: Cannot get configuration file with https, will try http...
[9936] 180331.170511.7628: ClientSetup: Download file Setup.cab from server
[9936] 180331.170511.7628: ClientSetup: Making web request: http://192.168.11.20//connect/default.aspx?Get=Setup.cab&LanguageId=1041&64bit=1
[9936] 180331.170512.0551: ClientSetup: Downloaded file C:\WINDOWS\Temp\ClientDeploymentTempFiles\Setup.cab
[9936] 180331.170512.0551: ClientSetup: The configuration cab is downloaded to C:\WINDOWS\Temp\ClientDeploymentTempFiles\Setup.cab
[9936] 180331.170512.2485: ClientSetup: Adding Server Info data in the Product Registry
[9936] 180331.170512.2745: DnsEnvironmentDetector: GetHostAddresses() returned 192.168.11.20, normal environment
[9936] 180331.170512.2824: ClientSetup: Exiting PreConfigTask.Run()
[9936] 180331.170512.2834: ClientSetup: Task with Id=ClientDeploy.PreConfiguration has TaskStatus=Success
[9936] 180331.170512.2834: ClientSetup: Task with Id=ClientDeploy.PreConfiguration has RebootStatus=NoReboot
[9936] 180331.170512.2834: ClientSetup: Exiting ConnectorWizardForm.RunTasks
[9936] 180331.170518.8868: ClientSetup: Running InstallRootCert Task at WizardPage DomainUserCred
[9936] 180331.170518.8868: ClientSetup: Entering ConnectorWizardForm.RunTasks
[9936] 180331.170518.8878: ClientSetup: Running Task with Id=ClientDeploy.InstallRootCertTask
[9936] 180331.170518.8898: ClientSetup: Entering InstallRootCertTask.Run
[9936] 180331.170518.8918: ClientSetup: Install root cert to local trusted store
[9936] 180331.170518.8979: ClientSetup: Exiting InstallRootCertTask.Run
[9936] 180331.170518.8988: ClientSetup: Task with Id=ClientDeploy.InstallRootCertTask has TaskStatus=Success
[9936] 180331.170518.8988: ClientSetup: Task with Id=ClientDeploy.InstallRootCertTask has RebootStatus=NoReboot
[9936] 180331.170518.8988: ClientSetup: Exiting ConnectorWizardForm.RunTasks
[9936] 180331.170518.8988: ClientSetup: Running SetupVPNAndDA Task at WizardPage DomainUserCred
[9936] 180331.170518.8988: ClientSetup: Entering ConnectorWizardForm.RunTasks
[9936] 180331.170518.8997: ClientSetup: Running Task with Id=ClientDeploy.SetupVpnAndDATask
[9936] 180331.170518.9048: ClientSetup: Entering SetupVpnAndDATask.Run
[9936] 180331.170518.9207: ClientSetup: Deploy VPN profile
[9936] 180331.170518.9287: VPN Client Utils: Error 632 returned from RasSetEntryProperties.
[9936] 180331.170518.9318: ClientSetup: RAS exception: 構造体のサイズが間違っています。
[9936] 180331.170518.9318: ClientSetup: Exting SetupVpnAndDATask.Run
[9936] 180331.170518.9318: ClientSetup: Task with Id=ClientDeploy.SetupVpnAndDATask has TaskStatus=Failed
[9936] 180331.170518.9318: ClientSetup: Task with Id=ClientDeploy.SetupVpnAndDATask has RebootStatus=NoReboot
[9936] 180331.170518.9327: ClientSetup: Exiting ConnectorWizardForm.RunTasks
[2888] 180331.170518.9426: ClientSetup: JoinNetwork Tasks returned TaskStatus=Failed
[2888] 180331.170521.6743: ClientSetup: Back from the Client Deployment Wizard
[2888] 180331.170521.6783: ClientSetup: Saving Wizard Data
[2888] 180331.170521.6813: ClientSetup: End of ClientDeploy: ErrorCode=1603

問題の箇所は、Bold体にした箇所で、VPN Profileの展開でエラーがでています。

Windows Server 2016 Essentialsでは、Anywhere Accessの機能にVPNの機能がありますが、ダッシュボードで以下のようにVPNを無効にすると、Client Connector もインストールが可能なります。

当面はこの方法で回避するしかなさそうです。