If you’ve built a custom sign in page in SharePoint 2010 but keep getting a 401 Unauthorized error instead of the sign in page then you’ve most probably deployed the solution package to a single web application.
FBA Custom Sign In Page returns 401…
If you’ve built a custom sign in page in SharePoint 2010 but keep getting a 401 Unauthorized error instead of the sign in page then you’ve most probably deployed the solution package to a single web application.