I have a SharePoint 2007 publishing portal that started throwing an error when user's click the Sign Out link. This started happening just this week and I can't tell what changes that have been made that caused this error. I've also noticed that links are no longer redirecting to the correct login page. I've set up FBA using the ADMembershipProvider, along with the LdapRoleProvider.
The direct link to the login page displays without error.
but a link to http://portal/ will redirect to http://portal/_layouts/Authenticate.aspx?Source=%2f and will displays "Unknown Error". Also, if I remove the query string parameter from the above link, http://portal/_layouts/useraccounts/login.aspx, this also throws an "Unknown Error".
Nothing is getting put in any of the Windows Event logs, but the SharePoint logs has this error.
Exception Type: System.Web.HttpException Exception Message: The referenced file '/_catalogs/masterpage/custommaster.master' is not allowed on this page.
This had been working previously, and there hasn't been any changes to the master file. I'm really stumped as to why this stopped working. If anyone has any idea's on what might be failing, that would be greatly appreciated.