New answers tagged iis
Your website is running outside of SharePoint and as such does not have SharePoint context. It knows nothing about anything going in SharePoint. I f you instantiate a new SPSite object from outside SharePoint in another site (running on the same server), whatever user the AppPool (or if impersonated, the user opening the webforms site), the current user ...
I saw this happening today after our SharePoint 2013 server was updated with the latest windows updates. I added the service accounts running the application pools to the local security policy "log on as a batch job" and started the app pools in IIS and that seemed to resolve the issue. SharePoint 2013: Service Account Configurations and Permissions
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