Concerning the error:
Could not find the specified key "Breadcrumb" or class id "PageResources".
The Breadcrumb widget that comes with Sitefinity 5.0 is not installed. To fix the error message go to Administration->Settings->Advanced->Toolboxes->Toolboxes->PageControls->Sections->Navigation->Tools->Breadcrumbs and delete the breadcrumb widget. Please to this at a test project first, This will let you access the page, but the breadcrumb widget will be missing.
Try installing the widget again.
Control CLR Type or Virtual Path: Telerik.Sitefinity.Web.UI.NavigationControls.Breadcrumb.Breadcrumb, Telerik.Sitefinity, Version=5.0.2472.0, Culture=neutral, PublicKeyToken=b28c218413bdf563
Global resource class ID:Global resource class ID
Check if the breadcrumb is working properly in the project.
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