DNN 9 - I have upgraded a site from 8.4 to 9.02

Now when I try to add a page, the Page Management page is empty.

When I try to edit the settings on a page, I get the message:

Error: is currently unavailable. DotNetNuke.Services.Exceptions.ModuleLoadException: The file '/DesktopModules/Admin/Tabs/ManageTabs.ascx' does not exist. ---> System.Web.HttpException: The file '/DesktopModules/Admin/Tabs/ManageTabs.ascx' does not exist. at System.Web.UI.Util.CheckVirtualFileExists(VirtualPath virtualPath) at System.Web.Compilation.BuildManager.GetVPathBuildResultInternal(VirtualPath virtualPath, Boolean noBuild, Boolean allowCrossApp, Boolean allowBuildInPrecompile, Boolean throwIfNotFound, Boolean ensureIsUpToDate) at System.Web.Compilation.BuildManager.GetVPathBuildResultWithNoAssert(HttpContext context, VirtualPath virtualPath, Boolean noBuild, Boolean allowCrossApp, Boolean allowBuildInPrecompile, Boolean throwIfNotFound, Boolean ensureIsUpToDate) at System.Web.UI.TemplateControl.LoadControl(VirtualPath virtualPath) at DotNetNuke.UI.ControlUtilities.LoadControl[T](TemplateControl containerControl, String ControlSrc) at DotNetNuke.UI.Modules.WebFormsModuleControlFactory.CreateModuleControl(TemplateControl containerControl, ModuleInfo moduleConfiguration) at DotNetNuke.UI.Modules.ModuleControlFactory.LoadModuleControl(TemplateControl containerControl, ModuleInfo moduleConfiguration) at DotNetNuke.UI.Modules.ModuleHost.LoadModuleControl() --- End of inner exception stack trace ---

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I'd sure appreciate any help any can offer