does anybody has solution for Below Error. i got this error when i have tried to access my web site after performing successfull upgrade from DNN 8.0.4 to Evoq DNN 9.0.2. ? please suggest solution. i have also recreate bin folder but unable to remove this error.

[NullReferenceException: Object reference not set to an instance of an object.]
   DotNetNuke.UI.Skins.Skin.GetSkin(PageBase page) +649
   DotNetNuke.Framework.DefaultPage.OnInit(EventArgs e) +87
   System.Web.UI.Control.InitRecursive(Control namingContainer) +139
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +408

[PageLoadException: Object reference not set to an instance of an object.]
   DotNetNuke.Services.Exceptions.Exceptions.ProcessPageLoadException(Exception exc, String URL) +451
   DotNetNuke.Framework.PageBase. (EventArgs e) +743
   System.Web.UI.Page.HandleError(Exception e) +84
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +6598
   System.Web.UI.Page.ProcessRequest(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +245
   System.Web.UI.Page.ProcessRequest() +72
   System.Web.UI.Page.ProcessRequestWithNoAssert(HttpContext context) +22
   System.Web.UI.Page.ProcessRequest(HttpContext context) +58
   ASP.default_aspx.ProcessRequest(HttpContext context) +4
   System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +188
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +69