Entity Framework: Illegal characters in path. (Connection String) (MVC3)

I just can't get this thing solved:

I'm trying to use the Entity Framework in my MVC3 project. But each time I call Entities context = new Entities(); I receive this error: Illegal characters in path. I do know this has something to do with my connectionstring, which is as follows:

metadata=res://*/Models.Model.csdl|res://*/Models.Model.ssdl|res://*/Models.Model.msl;provider=System.Data.SqlClient;provider connection string="Data Source=.\SQLEXPRESS;Initial Catalog=databasename;Persist Security Info=True;User ID=username;Password=password;MultipleActiveResultSets=True"

I used Reflector to find out whether the resources where properly embedded in my assembly, and the answer is yes they are perfectly embedded in my assembly as Models.Model.csdl, .ssdl and .msl...

My Model is in the same assembly as were I'm trying to connect, and is NOT referenced, which means that the wildcard * should just work fine.

The ConnectionString is exactly the same as generated by the wizard...

[ArgumentException: Illegal characters in path.]
   System.IO.Path.CheckInvalidPathChars(String path) +142
   System.IO.Path.Combine(String path1, String path2) +46
   System.Web.Compilation.DiskBuildResultCache.GetBuildResult(String cacheKey, VirtualPath virtualPath, Int64 hashCode, Boolean ensureIsUpToDate) +41
   System.Web.Compilation.BuildManager.GetBuildResultFromCacheInternal(String cacheKey, Boolean keyFromVPP, VirtualPath virtualPath, Int64 hashCode, Boolean ensureIsUpToDate) +237
   System.Web.Compilation.BuildManager.GetVPathBuildResultFromCacheInternal(VirtualPath virtualPath, Boolean ensureIsUpToDate) +162
   System.Web.Compilation.BuildManager.GetVPathBuildResultInternal(VirtualPath virtualPath, Boolean noBuild, Boolean allowCrossApp, Boolean allowBuildInPrecompile, Boolean throwIfNotFound, Boolean ensureIsUpToDate) +91
   System.We开发者_运维问答b.Compilation.BuildManager.GetVPathBuildResultWithNoAssert(HttpContext context, VirtualPath virtualPath, Boolean noBuild, Boolean allowCrossApp, Boolean allowBuildInPrecompile, Boolean throwIfNotFound, Boolean ensureIsUpToDate) +203
   System.Web.Compilation.BuildManager.GetObjectFactory(String virtualPath, Boolean throwIfNotFound) +180
   System.Web.Mvc.BuildManagerWrapper.System.Web.Mvc.IBuildManager.FileExists(String virtualPath) +18
   System.Web.Mvc.VirtualPathProviderViewEngine.GetPathFromGeneralName(ControllerContext controllerContext, List`1 locations, String name, String controllerName, String areaName, String cacheKey, String[]& searchedLocations) +228
   System.Web.Mvc.VirtualPathProviderViewEngine.GetPath(ControllerContext controllerContext, String[] locations, String[] areaLocations, String locationsPropertyName, String name, String controllerName, String cacheKeyPrefix, Boolean useCache, String[]& searchedLocations) +492
   System.Web.Mvc.VirtualPathProviderViewEngine.FindView(ControllerContext controllerContext, String viewName, String masterName, Boolean useCache) +198
   System.Web.Mvc.<>c__DisplayClassc.<FindView>b__b(IViewEngine e) +47
   System.Web.Mvc.ViewEngineCollection.Find(Func`2 lookup, Boolean trackSearchedPaths) +177
   System.Web.Mvc.ViewResult.FindView(ControllerContext context) +144
   System.Web.Mvc.ViewResultBase.ExecuteResult(ControllerContext context) +151
   System.Web.Mvc.<>c__DisplayClass1c.<InvokeActionResultWithFilters>b__19() +33
   System.Web.Mvc.ControllerActionInvoker.InvokeActionResultFilter(IResultFilter filter, ResultExecutingContext preContext, Func`1 continuation) +784900
   System.Web.Mvc.ControllerActionInvoker.InvokeActionResultWithFilters(ControllerContext controllerContext, IList`1 filters, ActionResult actionResult) +265
   System.Web.Mvc.ControllerActionInvoker.InvokeAction(ControllerContext controllerContext, String actionName) +784976
   System.Web.Mvc.Controller.ExecuteCore() +159
   System.Web.Mvc.ControllerBase.Execute(RequestContext requestContext) +335
   System.Web.Mvc.<>c__DisplayClassb.<BeginProcessRequest>b__5() +62
   System.Web.Mvc.Async.<>c__DisplayClass1.<MakeVoidDelegate>b__0() +20
   System.Web.Mvc.<>c__DisplayClasse.<EndProcessRequest>b__d() +54
   System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +453
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +371

It doesn't even show the ActionResult where the problem is occuring...

Finally, after removing the backslash in SERVERNAME\INSTANCE it started working. (added a alias to my SQL Server Instance without a backslash in it). Probably can be solved as well by removing the backslash from illegal characters using the web.config...how it ever got on that list remains unknown