Website and CMS not Accessable, Server Error in '/'

Came into work this morning, and found out that nobody can access our website. I tried to log into the CMS to see if something was up there, but I cannot access the CMS either. Anytime I try to access the CMS or website i receive a "Server Error in '/' Application." error. Full error details are listed below.

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.Dictionary`2.Insert(TKey key, TValue value, Boolean add) +14643456 Telerik.Sitefinity.Configuration.ConfigElementDictionary`2.Add(TKey key, TElement element) +194 Telerik.Sitefinity.Security.Configuration.SecurityConfig.LoadDefaults() +24853 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() +1133 Telerik.Sitefinity.Abstractions.Bootstrapper.RegisterRoutes() +824 Telerik.Sitefinity.Abstractions.Bootstrapper.Bootstrap() +560 Telerik.Sitefinity.Web.SitefinityHttpModule.Init(HttpApplication context) +239 System.Web.HttpApplication.RegisterEventSubscriptionsWithIIS(IntPtr appContext, HttpContext context, MethodInfo[] handlers) +583 System.Web.HttpApplication.InitSpecial(HttpApplicationState state, MethodInfo[] handlers, IntPtr appContext, HttpContext context) +169 System.Web.HttpApplicationFactory.GetSpecialApplicationInstance(IntPtr appContext, HttpContext context) +396 System.Web.Hosting.PipelineRuntime.InitializeApplication(IntPtr appContext) +333 [HttpException (0x80004005): The type initializer for 'Telerik.Sitefinity.Security.SecurityManager' threw an exception.] System.Web.HttpRuntime.FirstRequestInit(HttpContext context) +525 System.Web.HttpRuntime.EnsureFirstRequestInit(HttpContext context) +124 System.Web.HttpRuntime.ProcessRequestNotificationPrivate(IIS7WorkerRequest wr, HttpContext context) +700

Hi Zach, it is very famous issue caused by .Net framework upgrade.  You can find more details how to fix it in this article: knowledgebase.progress.com/.../sitefinity-and-net-4-7-compatibility-issues