Windows 10 Creators Update (and therefore I'm assuming NET Framework 4.7) has broken my ASP.NET site running on Sitefinity (somewhat old - 8.0.5710).

Is there any way to downgrade .NET Framework (uninstall 4.7) in Windows 10?

I've tried a lot of things and the site throws an error in Cassini, IIS and IIS Express. I ran out of ideas what could be wrong after a good few days of investigating and decided to spin up a VM without Creators Update. Installed IIS and deployed the site, which was working. I then installed Creators Update and right after the installation launched the site.

Here's what I get:
`Server Error in '/' Application.

An item with the same key has already been added.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.ArgumentException: An item with the same key has already been added.

Source Error:

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

Stack Trace:

[ArgumentException: An item with the same key has already been added.]
System.ThrowHelper.ThrowArgumentException(ExceptionResource resource) +56
System.Collections.Generic.Dictionary2.Insert(TKey key, TValue value, Boolean add) +14643456 Telerik.Sitefinity.Configuration.ConfigElementDictionary2.Add(TKey key, TElement element) +194
Telerik.Sitefinity.Security.Configuration.SecurityConfig.LoadDefaults() +2235
Telerik.Sitefinity.Security.Configuration.SecurityConfig.OnPropertiesInitialized() +92
Telerik.Sitefinity.Configuration.ConfigSection.InitializeProperties() +27
Telerik.Sitefinity.Configuration.ConfigElement.EnsurePropertiesInitialized() +122
Telerik.Sitefinity.Configuration.ConfigElement.get_Properties() +21
Telerik.Sitefinity.Configuration.Data.XmlConfigProvider.LoadAttributes(ConfigElement element, XmlReader reader, ConfigPolicyHandler policyHandler, String policyName, UpgradingInfo upgradingInfo, Boolean isNew) +214
Telerik.Sitefinity.Configuration.Data.XmlConfigProvider.LoadElement(ConfigElement element, XmlReader reader, ConfigPolicyHandler policyHandler, String policyName, UpgradingInfo upgradingInfo, Boolean isNew, Boolean validateTagName) +198
Telerik.Sitefinity.Configuration.Data.XmlConfigProvider.LoadSectionFromReader(ConfigSection section, XmlReader reader, ConfigPolicyHandler policyHandler, String policyName, Boolean checkForUpgrade, UpgradingInfo& upgradingInfo) +240
Telerik.Sitefinity.Configuration.Data.XmlConfigProvider.LoadSectionFromFile(ConfigSection section, ConfigPolicyHandler policyHandler, String policyName, Boolean withUpgrade) +134
Telerik.Sitefinity.Configuration.Data.XmlConfigProvider.LoadSection(ConfigSection section, ConfigPolicyHandler policyHandler, String policyName) +72
Telerik.Sitefinity.Configuration.ConfigSection.Initialize(ConfigProvider provider, ConfigPolicyHandler policyHandler, String policyName, Boolean singlePolicy) +301
Telerik.Sitefinity.Configuration.ConfigSection.Initialize(ConfigProvider provider) +28
Telerik.Sitefinity.Configuration.Config.GetSectionInternal(Type sectionType, Boolean safeMode, String sectionName) +168
Telerik.Sitefinity.Configuration.Config.GetSectionPrivate(Type sectionType, Boolean safeMode, String sectionName) +178
Telerik.Sitefinity.Configuration.Config.GetSectionPrivate(Boolean safeMode) +99
Telerik.Sitefinity.Security.SecurityManager..cctor() +369

[TypeInitializationException: The type initializer for 'Telerik.Sitefinity.Security.SecurityManager' threw an exception.]
Telerik.Sitefinity.Security.SecurityManager.GetCurrentUserId() +0
Telerik.Sitefinity.Services.SitefinityContextBase.get_BackendCulture() +152
Telerik.Sitefinity.Localization.Resource.ResolveCulture(CultureInfo culture) +59
Telerik.Sitefinity.Localization.Resource.GetString(ResourceDataProvider provider, String classId, ResourceProperty property, CultureInfo culture, Boolean falback) +81
Telerik.Sitefinity.Modules.ControlTemplates.ControlTemplates.RegisterTemplatableControl(Type controlType, Type dataItemType, String resourceClassId, String areaName, String controlDisplayName) +162
Telerik.Sitefinity.Modules.ControlTemplates.ControlTemplates.RegisterTemplatableControl(Type controlType, Type dataItemType) +110
Telerik.Sitefinity.Services.SystemManager.Initialize() +1234
Telerik.Sitefinity.Abstractions.Bootstrapper.RegisterRoutes() +1027
Telerik.Sitefinity.Abstractions.Bootstrapper.Bootstrap() +593
Telerik.Sitefinity.Web.SitefinityHttpModule.Init(HttpApplication context) +259
System.Web.HttpApplication.RegisterEventSubscriptionsWithIIS(IntPtr appContext, HttpContext context, MethodInfo[] handlers) +612
System.Web.HttpApplication.InitSpecial(HttpApplicationState state, MethodInfo[] handlers, IntPtr appContext, HttpContext context) +172
System.Web.HttpApplicationFactory.GetSpecialApplicationInstance(IntPtr appContext, HttpContext context) +421
System.Web.Hosting.PipelineRuntime.InitializeApplication(IntPtr appContext) +359

[HttpException (0x80004005): The type initializer for 'Telerik.Sitefinity.Security.SecurityManager' threw an exception.]
System.Web.HttpRuntime.FirstRequestInit(HttpContext context) +534
System.Web.HttpRuntime.EnsureFirstRequestInit(HttpContext context) +117
System.Web.HttpRuntime.ProcessRequestNotificationPrivate(IIS7WorkerRequest wr, HttpContext context) +726

Version Information: Microsoft .NET Framework Version:4.0.30319; ASP.NET Version:4.7.2046.0`

This looks like a config parsing issue but I am out of ideas where to look next and how to pinpoint the exact problem?

.NET Framework 4.7 Feedback #393

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