Logging into the admin just redirects you to the login page. It does not give you an error. It just simply returns you to the login page.
1) I have checked the telerik_Users table and everything appears to be fine. No user is locked out and it shows no failed attempt for any user. We have tried multiple users and all users in the database are experiencing this problem. Trying an invalid user displays the expected validation error.
2) I have tried going to a page in the admin after logging on (/sitefinity/admin/pages.aspx, /sitefinity/admin/modules.aspx, etc.). They all return you to the login page.
3) I have checked the Sitefinity.log file. It doesn't have any errors logged since this has started happening. I have also checked all of the event logs. They do not show any errors or warnings either.
4) I have tried changing the ReturnURL query string parameter to multiple valid files and multiple invalid files. All of the valid files just return you to the login page, but the invalid files actually throw a 'Resource cannot be found' error. After receiving that error, I have tried to go to valid pages and they return you to the login page.
5) We have several developer workstations, a testing server, a staging server, and a production server. This problem only occurs on the production server. We have not made any changes (other than content on pages) to the production server in months and this issue just started happening today.
Does anyone have any suggestions or ideas regarding this problem?