A static HTML website I look after is hosted on a Windows Server 2012R2 instance running IIS, it makes use of a web.config file as it has some settings that allow this site to be served from behind an Amazon Web Services Elastic Load Balancer.
Today it kept crashing with the thousands of these events in event viewer:
Event code: 3008 Event message: A configuration error has occurred. Event time: 05/03/2020 09:15:49 Event time (UTC): 05/03/2020 09:15:49 Event ID: 83032f1dc8d9486e95dfc13f9f88a22d Event sequence: 1 Event occurrence: 1 Event detail code: 0 Application information: Application domain: /LM/W3SVC/6/ROOT-1789-132278733487264657 Trust level: Full Application Virtual Path: / Application Path: C:\Sites\your-website.com\static\ Machine name: PRODUCTION-WEB- Process information: Process ID: 2104 Process name: w3wp.exe Account name: IIS APPPOOL\your-website.com Exception information: Exception type: ConfigurationErrorsException Exception message: Unrecognized attribute 'targetFramework'. Note that attribute names are case-sensitive. (C:\Sites\your-website.com\static\web.config line 4) Request information: Request URL: http://www.your-website.com/default.aspx Request path: /default.aspx User host address: 172.31.38.122 User: Is authenticated: False Authentication Type: Thread account name: IIS APPPOOL\your-website.com Thread information: Thread ID: 5 Thread account name: IIS APPPOOL\your-website.com Is impersonating: False Stack trace: at System.Web.HttpRuntime.HostingInit(HostingEnvironmentFlags hostingFlags) Custom event details: 
The fix was to change the websites application pool to use .NET CLR Version 4 rather than .NET CLR Version 2
So, open IIS, choose Application Pools from the left-hand navigation, Choose your app pool and click basic settings to open the dialog to change which .NET CLR Version to use.
Once this was done the errors stopped and the site stopped crashing
Success 🎉
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