Problem opening an old project and sitefinity error

Hello,

I've to do some modification on a 5 years old project made with sitefinity, I've re-opened the solution from the svn, created a local copy from the production DB) and corrected the pointment.

When I launch the followind error

 Invalid attribute "authenticationMode" for element "Telerik.Sitefinity.Security.Configuration.SecurityConfig". 

and here's a part of the stacktrace

[ConfigurationErrorsException: Invalid attribute "authenticationMode" for element "Telerik.Sitefinity.Security.Configuration.SecurityConfig". ] Telerik.Sitefinity.Configuration.Data.XmlConfigProvider.LoadAttributes(ConfigElement element, XmlReader reader, ConfigPolicyHandler policyHandler, String policyName, Boolean isUpgrading, Boolean isNew) +753 Telerik.Sitefinity.Configuration.Data.XmlConfigProvider.LoadElement(ConfigElement element, XmlReader reader, ConfigPolicyHandler policyHandler, String policyName, Boolean isUpgrading, Version upgradeFrom, Boolean isNew, Boolean validateTagName) +243 Telerik.Sitefinity.Configuration.Data.XmlConfigProvider.LoadSection(ConfigSection section, ConfigPolicyHandler policyHandler, String policyName) +537 Telerik.Sitefinity.Configuration.ConfigSection.Initialize(ConfigProvider provider, ConfigPolicyHandler policyHandler, String policyName, Boolean singlePolicy) +211 Telerik.Sitefinity.Configuration.ConfigProvider.GetSection(ConfigPolicyHandler policyHandler, String policyName) +170 Telerik.Sitefinity.Security.SecurityManager..cctor() +180 [TypeInitializationException: The type initializer for 'Telerik.Sitefinity.Security.SecurityManager' threw an exception.] Telerik.Sitefinity.Abstractions.Exceptions.HandleException(Exception exceptionToHandle, ExceptionPolicyName policy, Exception& exceptionToThrow) +234 Telerik.Sitefinity.Abstractions.Exceptions.HandleException(Exception exceptionToHandle, ExceptionPolicyName policy) +23 Telerik.Sitefinity.Data.ManagerBase`1.Initialize() +787 Telerik.Sitefinity.Data.ManagerBase`1..ctor(String providerName, String transactionName) +34 Telerik.Sitefinity.Localization.Res..cctor() +28 [TypeInitializationException: The type initializer for 'Telerik.Sitefinity.Localization.Res' threw an exception.] Telerik.Sitefinity.Localization.Res.RegisterResource() +0 Telerik.Sitefinity.Abstractions.ObjectFactory.RegisterStringResources() +108 Telerik.Sitefinity.Abstractions.ObjectFactory.RegisterIoCTypes() +226 Telerik.Sitefinity.Abstractions.Bootstrapper.Bootstrap() +226 Telerik.Sitefinity.Web.SitefinityHttpModule.Init(HttpApplication context) +157 System.Web.HttpApplication.RegisterEventSubscriptionsWithIIS(IntPtr appContext, HttpContext context, MethodInfo[] handlers) +530 System.Web.HttpApplication.InitSpecial(HttpApplicationState state, MethodInfo[] handlers, IntPtr appContext, HttpContext context) +304 System.Web.HttpApplicationFactory.GetSpecialApplicationInstance(IntPtr appContext, HttpContext context) +404 System.Web.Hosting.PipelineRuntime.InitializeApplication(IntPtr appContext) +475 [HttpException (0x80004005): The type initializer for 'Telerik.Sitefinity.Localization.Res' threw an exception.] System.Web.HttpRuntime.FirstRequestInit(HttpContext context) +12618692 System.Web.HttpRuntime.EnsureFirstRequestInit(HttpContext context) +159 System.Web.HttpRuntime.ProcessRequestNotificationPrivate(IIS7WorkerRequest wr, HttpContext context) +12458309

What am I doing wrong? I've got no files in Logs folder

Thanks​