The cluster either has not been verified or there are errors or failures in the verification report

sometime when you add a node to the cluster you get below error:-

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Rule Check Result

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Rule "Microsoft Cluster Service (MSCS) cluster verification errors" failed.

The cluster either has not been verified or there are errors or failures in the verification report. Refer to KB953748 or SQL Server Books Online for more information.

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OK  

You will get error like this:-

Workaround: -

To work around this issue, you must fix the problem that caused validation to fail. If you can determine that the problem that caused validation to fail can be fixed later, you might want to use the command line installation option in this article to ignore the error message, and to try to install the SQL Server 2008 failover cluster instance. If you do this, before using the system again you must still fix the underlying problem that caused validation to fail.

Note If you try this command line installation option and SQL Server Setup fails, make sure that the cluster hardware configuration is valid, and then contact Microsoft Customer Support Services (CSS) for more help.

At a command prompt, change to the hard disk drive and to the folder that contains SQL Server Setup (Setup.exe). Then, type one of the following commands to skip the validation rule:

For an integrated failover Add-Note setup, run the following command on each node that is being added:

   Setup /SkipRules=Cluster_VerifyForErrors /Action=InstallFailoverCluster

For an advanced or enterprise installation, run the following command:

    Setup /SkipRules=Cluster_VerifyForErrors /Action=CompleteFailoverCluster

If you receive this validation failure when you add a node to an existing failover installation, run the following command on each node that is being added:

    Setup /SkipRules=Cluster_VerifyForErrors /Action=AddNode

Note Setting up a SQL Server 2008 failover cluster instance on a Windows Server 2008-based failover cluster that contains errors in the Windows Server 2008 Cluster Validation Report is unsupported. For a SQL Server 2008 failover cluster instance to be in a supported scenario, the Windows Server 2008 Cluster Validation Report cannot contain errors. Confirm with Microsoft CSS that the cluster configuration is in a supported state.