SP 2013 FBA Authentication failure: the http request is unauthorized with client authentication scheme 'negotiate'

I get the following error on the event viewer when trying to log on a Sharepoint website with forms-based authentication (FBA):

The http request is unauthorized with client authentication scheme 'negotiate'. The authentication header received from the server was ''.

Details

• 
  

  I've configured FBA using this tutorial (http://ift.tt/1hOr2Qw)

  
  


• 
  

  On IIS, the website's authentication is configured to only use forms-based authentitcation.

  
  


• 
  

  Central Admin is configured to use Windows Authentication and ASP.NET Impersonation.

  
  


• 
  

  Security Token Service is configured to only use forms-based authentitcation.