Just did a plain vanilla install of Umbraco 6.0.4 CMS via NuGet.
Running on .NET 4.0 with IIS Express under Visual Studio 2012.
Database is a local SQL Server 10.50.1617.

I get this error immediately after installing uSync 1.1.2:

Could not load type 'Umbraco.Web.IApplicationEventHandler' from assembly 'umbraco, Version=1.0.4863.23141, Culture=neutral, PublicKeyToken=null'.

Stack trace:

[TypeLoadException: Could not load type 'Umbraco.Web.IApplicationEventHandler' from assembly 'umbraco, Version=1.0.4863.23141, Culture=neutral, PublicKeyToken=null'.]
   System.Reflection.RuntimeAssembly.GetExportedTypes(RuntimeAssembly assembly, ObjectHandleOnStack retTypes) +0
   System.Reflection.RuntimeAssembly.GetExportedTypes() +21
   Umbraco.Core.TypeFinder.GetTypesWithFormattedException(Assembly a) +68
   Umbraco.Core.TypeFinder.GetTypes(Type assignTypeFrom, IEnumerable`1 assemblies, Boolean onlyConcreteClasses) +129
   Umbraco.Core.TypeFinder.GetAssignablesFromType(IEnumerable`1 assemblies, Boolean onlyConcreteClasses) +56
   Umbraco.Core.TypeFinder.FindClassesOfType(IEnumerable`1 assemblies, Boolean onlyConcreteClasses) +59
   Umbraco.Core.TypeFinder.FindClassesOfType(IEnumerable`1 assemblies) +45
   Umbraco.Core.PluginManager.<ResolveTypes>b__1c() +55
   Umbraco.Core.PluginManager.LoadViaScanningAndUpdateCacheFile(TypeList typeList, TypeResolutionKind resolutionKind, Func`1 finder) +46
   Umbraco.Core.PluginManager.ResolveTypes(Func`1 finder, TypeResolutionKind resolutionType, Boolean cacheResult) +1169
   Umbraco.Core.PluginManager.ResolveTypes(Boolean cacheResult) +133
   Umbraco.Core.CoreBootManager.InitializeApplicationEventsResolver() +44
   Umbraco.Web.WebBootManager.InitializeApplicationEventsResolver() +8
   Umbraco.Core.CoreBootManager.Initialize() +444
   Umbraco.Web.WebBootManager.Initialize() +18
   Umbraco.Core.UmbracoApplicationBase.StartApplication(Object sender, EventArgs e) +79
   Umbraco.Core.UmbracoApplicationBase.Application_Start(Object sender, EventArgs e) +9
[HttpException (0x80004005): Could not load type 'Umbraco.Web.IApplicationEventHandler' from assembly 'umbraco, Version=1.0.4863.23141, Culture=neutral, PublicKeyToken=null'.]
   System.Web.HttpApplicationFactory.EnsureAppStartCalledForIntegratedMode(HttpContext context, HttpApplication app) +9859441
   System.Web.HttpApplication.RegisterEventSubscriptionsWithIIS(IntPtr appContext, HttpContext context, MethodInfo[] handlers) +118
   System.Web.HttpApplication.InitSpecial(HttpApplicationState state, MethodInfo[] handlers, IntPtr appContext, HttpContext context) +172
   System.Web.HttpApplicationFactory.GetSpecialApplicationInstance(IntPtr appContext, HttpContext context) +336
   System.Web.Hosting.PipelineRuntime.InitializeApplication(IntPtr appContext) +296
[HttpException (0x80004005): Could not load type 'Umbraco.Web.IApplicationEventHandler' from assembly 'umbraco, Version=1.0.4863.23141, Culture=neutral, PublicKeyToken=null'.]
   System.Web.HttpRuntime.FirstRequestInit(HttpContext context) +9873784
   System.Web.HttpRuntime.EnsureFirstRequestInit(HttpContext context) +101
   System.Web.HttpRuntime.ProcessRequestNotificationPrivate(IIS7WorkerRequest wr, HttpContext context) +254

Any clues? :-)