"Value cannot be null" Error on Sitefinity Backend Log-in Page
I randomly started receiving a "Value cannot be null exception" when trying to access the Sitefinity backend log-in screen (see attached screenshot). I receive this error for both of the following cases:
http://localhost:37499/site/Sitefinity/Authenticate/SWT?realm=... (redirected from other page)
I can't pinpoint exactly when it started happening, but it was soon after I changed the permissions of a page to Authenticated users. I have since reverted this change but am still experiencing the issue. I now have to use the log-in page I created within my web site and log-in as an Administrator in order to do any backend administration.
My site is running on Sitefinity 5.1.3210.0 with IIS 7 (via Sitefinity Project Manager) and using Claims Authentication.
I have searched the forums and found the following thread which seems like the same issue I am experiencing. However, none of the suggested solutions seem relevant in my case.