Today, we noticed that one of our Web servers in SharePoint 2013 Enterprise farm started showing up ‘Upgrade Required’ status. Closer look at it says that Microsoft.SharePoint.Administration.SPIisWebSite type object needs upgrade.
We are sure that, no updates are applied to SharePoint servers which needs psconfig to be run.All the servers received same updates, but just one server is requesting for psconfig to be run. That made me think that something exclusively is wrong or different with this server.
I did not trust the UI at first and tried the following PowerShell command to find the status of upgrade.
which returned False, confirming that we do not need to run psconfig.
It ran upgrade checks on content databases, site collections and some other components and complained that object of type Microsoft.SharePoint.Administration.SPIisWebSite needs upgrade.
Root cause of issue was found after comparing IIS with other servers. Recently while troubleshooting we created a test web application and deleted it later. But it was still hanging on in IIS of this server. After deleting that web application site and application pool from IIS, the error disappeared.