Strange error happens sometimes at backup start - smartcard certificate

[Dieter]

I have a scheduled backup in Veeam Agent for Windows (Win 11) which runs once per day. It is doing the backup to a CIFS network location on a Synology NAS. The backup works fine most of the times. However "sometimes" it is failing with a strange error message citing that there was a problem with a non-trustworthy certificate authority of a smartcard certificate:

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("Agent Backup job: Job Voyager5  Veeam Agent for Microsoft Windows  Error Saturday, 04 January 2025 22:35:35 Error: [Voyager5] Failed to get disk free space. Beim Verarbeiten des Smartcard-Zertifikats für die Authentifizierung wurde eine nicht vertrauenswürdige Zertifizierungsstelle gefunden. Wenden Sie sich an den Systemadministrator Failed to get free space on disk '\\Lynx\BU_Voyager5'")

This error is strange for a couple of reasons:
a) I am using normal userid / password authentication against the SMB drive - so where is a smartcard certificate involved in the process at all?
b) At the next retry the job runs successfull - so that "non-trustworthy" certificate authority issue is gone without any change? But a couple of days later I will get the same problem again ...
c) I have another Win11 system which uses Veeam Agent for Windows to backup against the same NAS with equivalent settings with no issues at all

I opened a support case (Case-Nr.07558893) for this - however I understand as I am using the free version I will just get email support on "best can do base" and haven't received any update since opening the case on Jan 5th ... .

Does anyone has any clue what this error message really means / what could cause it? I am actually not sure whether the error message itself is correct or a translation error. The displayed error message on my german installation is

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"Agent Backup job: Job Voyager5  Veeam Agent for Microsoft Windows  Error Saturday, 04 January 2025 22:35:35 Error: [Voyager5] Failed to get disk free space. Beim Verarbeiten des Smartcard-Zertifikats für die Authentifizierung wurde eine nicht vertrauenswürdige Zertifizierungsstelle gefunden. Wenden Sie sich an den Systemadministrator Failed to get free space on disk '\\Lynx\BU_Voyager5'".

When I try to re-translate this to english it would sound like

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"Agent Backup job: Job Voyager5  Veeam Agent for Microsoft Windows  Error Saturday, 04 January 2025 22:35:35 Error: [Voyager5] Failed to get disk free space. While processing the smartcard certificate for authentication there was a non-trustworthy certificate authority found. Please contact your system administrator. Failed to get free space on disk '\\Lynx\BU_Voyager5'"

These are the relevant entries from the log file:

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[08.01.2025 01:17:25] <01> Info     [Voyager5] [FC] Setting share credentials: Share \\Lynx\BU_Voyager5, User .\xxx_redacted_user
[08.01.2025 01:17:25] <01> Info     Physical host volume was not found for path '\\Lynx\BU_Voyager5' on host 'This server'.
[08.01.2025 01:17:25] <01> Info     [Voyager5] [FC] Getting disk free space: path: '\\Lynx\BU_Voyager5'
[08.01.2025 01:18:25] <01> Error    Retrieved incorrect string: do rpc - Beim Verarbeiten des Smartcard-Zertifikats für die Authentifizierung wurde eine nicht vertrauenswürdige Zertifizierungsstelle gefunden. Wenden Sie sich an den Systemadministrator
[08.01.2025 01:18:25] <01> Error    Failed to get free space on disk '\\Lynx\BU_Voyager5'
[08.01.2025 01:18:25] <01> Error    --tr:Error code: 0x80090352
[08.01.2025 01:18:25] <01> Error    --tr:Failed to call DoRpc. CmdName: [FcGetDiskFreeSpace].
[08.01.2025 01:18:25] <01> Error    Failed to call RPC function 'FcGetDiskFreeSpace'. InParams: '<InputArguments><Path value="\\Lynx\BU_Voyager5" /></InputArguments>'. 
[08.01.2025 01:18:25] <01> Error    Beim Verarbeiten des Smartcard-Zertifikats für die Authentifizierung wurde eine nicht vertrauenswürdige Zertifizierungsstelle gefunden. Wenden Sie sich an den Systemadministrator
[08.01.2025 01:18:25] <01> Error    Failed to get free space on disk '\\Lynx\BU_Voyager5'
[08.01.2025 01:18:25] <01> Error     (System.ApplicationException)
[08.01.2025 01:18:25] <01> Error       bei Veeam.Backup.ProxyProvider.CNativeAccessor.GenerateExceptionWithoutTrace(Exception ex)
[08.01.2025 01:18:25] <01> Error       bei Veeam.Backup.ProxyProvider.CNativeAccessor.CheckString(String value, String message)
[08.01.2025 01:18:25] <01> Error       bei Veeam.Backup.ProxyProvider.CProxyRpcInvoker.Call(String methodName, CProxyInvokeInputArg inputArgs, Boolean secureCall)
[08.01.2025 01:18:25] <01> Error    [Voyager5] Failed to get disk free space. (System.Exception)
[08.01.2025 01:18:25] <01> Error       bei Veeam.Backup.ProxyProvider.CProxyFileCommander.GetDiskFreeSpace(String path)
[08.01.2025 01:18:25] <01> Error       bei Veeam.Backup.Core.CWinFileCommander.FindDirInfo(String link)
[08.01.2025 01:18:25] <01> Error       bei Veeam.EndPoint.CCifsShareRepositoryAvailabilityChecker.TryCheckAvailability(Exception& exception)
[08.01.2025 01:18:25] <01> Error    Beim Verarbeiten des Smartcard-Zertifikats für die Authentifizierung wurde eine nicht vertrauenswürdige Zertifizierungsstelle gefunden. Wenden Sie sich an den Systemadministrator
[08.01.2025 01:18:25] <01> Error    Failed to get free space on disk '\\Lynx\BU_Voyager5'
[08.01.2025 01:18:25] <01> Error     (System.ApplicationException)
[08.01.2025 01:18:25] <01> Error       bei Veeam.Backup.ProxyProvider.CNativeAccessor.GenerateExceptionWithoutTrace(Exception ex)
[08.01.2025 01:18:25] <01> Error       bei Veeam.Backup.ProxyProvider.CNativeAccessor.CheckString(String value, String message)
[08.01.2025 01:18:25] <01> Error       bei Veeam.Backup.ProxyProvider.CProxyRpcInvoker.Call(String methodName, CProxyInvokeInputArg inputArgs, Boolean secureCall)
[08.01.2025 01:18:25] <01> Error    Beim Verarbeiten des Smartcard-Zertifikats für die Authentifizierung wurde eine nicht vertrauenswürdige Zertifizierungsstelle gefunden. Wenden Sie sich an den Systemadministrator
[08.01.2025 01:18:25] <01> Error     (Veeam.Backup.Common.CCppComponentException)
[08.01.2025 01:18:25] <01> Error    Failed to get free space on disk '\\Lynx\BU_Voyager5'
[08.01.2025 01:18:25] <01> Error     (Veeam.Backup.Common.CCppComponentException)
[08.01.2025 01:18:25] <01> Info     [EpBackupCacheStrategy] Repository is not accessible
[08.01.2025 01:18:26] <01> Info     [CBackupTaskContext] Disposing backup task context
[08.01.2025 01:18:26] <01> Error    [Voyager5] Failed to get disk free space. (System.Exception)
[08.01.2025 01:18:26] <01> Error       bei Veeam.Backup.ProxyProvider.CProxyFileCommander.GetDiskFreeSpace(String path)
[08.01.2025 01:18:26] <01> Error       bei Veeam.Backup.Core.CWinFileCommander.FindDirInfo(String link)
[08.01.2025 01:18:26] <01> Error       bei Veeam.EndPoint.CCifsShareRepositoryAvailabilityChecker.TryCheckAvailability(Exception& exception)
[08.01.2025 01:18:26] <01> Error    --- Ende der Stapelüberwachung vom vorhergehenden Ort, an dem die Ausnahme ausgelöst wurde ---
[08.01.2025 01:18:26] <01> Error       bei System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
[08.01.2025 01:18:26] <01> Error       bei Veeam.EndPoint.CDisabledBackupCacheStrategy..ctor(CBackupTaskContext taskContext, Boolean clearDigestsOnSuccess)
[08.01.2025 01:18:26] <01> Error       bei Veeam.EndPoint.CBackupCacheStrategyFactory.Create(CBackupTaskContext taskContext, IStopSessionSync sessControl, CShadowVolumesLayoutCache volumesLayoutCache)
[08.01.2025 01:18:26] <01> Error       bei Veeam.EndPoint.CEndPointBackupJobPerformer.Perform(CBackupTaskSession backupSession, CShadowVolumesLayout layout, CEpLicenseEdition licenseEdition, CSessionEpDiskFilter sessionDiskFilter)
[08.01.2025 01:18:26] <01> Error       bei Veeam.EndPoint.CEndPointBackupJobPerformer.Perform()
[08.01.2025 01:18:26] <01> Error    Beim Verarbeiten des Smartcard-Zertifikats für die Authentifizierung wurde eine nicht vertrauenswürdige Zertifizierungsstelle gefunden. Wenden Sie sich an den Systemadministrator
[08.01.2025 01:18:26] <01> Error    Failed to get free space on disk '\\Lynx\BU_Voyager5'
[08.01.2025 01:18:26] <01> Error     (System.ApplicationException)
[08.01.2025 01:18:26] <01> Error       bei Veeam.Backup.ProxyProvider.CNativeAccessor.GenerateExceptionWithoutTrace(Exception ex)
[08.01.2025 01:18:26] <01> Error       bei Veeam.Backup.ProxyProvider.CNativeAccessor.CheckString(String value, String message)
[08.01.2025 01:18:26] <01> Error       bei Veeam.Backup.ProxyProvider.CProxyRpcInvoker.Call(String methodName, CProxyInvokeInputArg inputArgs, Boolean secureCall)
[08.01.2025 01:18:26] <01> Error    Beim Verarbeiten des Smartcard-Zertifikats für die Authentifizierung wurde eine nicht vertrauenswürdige Zertifizierungsstelle gefunden. Wenden Sie sich an den Systemadministrator
[08.01.2025 01:18:26] <01> Error     (Veeam.Backup.Common.CCppComponentException)
[08.01.2025 01:18:26] <01> Error    Failed to get free space on disk '\\Lynx\BU_Voyager5'
[08.01.2025 01:18:26] <01> Error     (Veeam.Backup.Common.CCppComponentException)
[08.01.2025 01:18:26] <01> Info     Set status 'Failed' for task session '877592f5-7436-409e-95db-3accdb908dc0', object name 'Voyager5'
[08.01.2025 01:18:26] <01> Info     Task session '877592f5-7436-409e-95db-3accdb908dc0' has been completed, status: 'Failed', '0' of '0' bytes, 

[david.domask]

Hi Dieter,

Thanks for the detailed write up and for sharing the case number. Indeed, Free/Community Edition products are supported on "best-effort" basis, so let's see if Support is able to work with this case.

At first blush though, not sure it's a Veeam issue. Do you see similar messages in the Event Log around those timestamps? I would check System, Application, and Security.

Similarly, a bit of searching did reveal a Synology user with a similar problem -- recreating the SMB share helped, but there was no root cause identified. Are you in a position to test with a new share? Seems like it might be some combination of Windows updates + Synology configuration, but the message itself is a Windows one, and it's unclear why it would be failing a check for Smartcards sometimes but not always. That there was very similar issue with another Synology user leads me to think it's about the Synology, but this is speculation of course.