Object reference not set to an instance of an object.
at SPSolutions.SharePoint.Delegation.ApplicationPages.ManUsrsInAuthStorePage.OnLoad(EventArgs e)
at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
This indicates that SharePoint is unable to find the Membership or Role provider in the web.config. Make sure that both the Extranet and Default zones include Membership and Role Provider sections as well as a ConnectionStrings section to connect to the membership store database and an entry in the PeoplePickerWildcards section referring to the Membership provider.
See Configuring a dual zone SharePoint site with FBA for specific details on editing the web.config files.