We have Kerberos installed in a Mendix application, but the service only work in our network with windows installations with IE 10. We configured SSO with Kerberos in Mendix with our corporate Active Directory. We have two A.D. users: one user for the keytab file and one user for running Mendix as a Service. Also we enabled SSO in Mendix by setting the after-startup microflow to the WinSSO.Start microflow. After starting the application as a service we see the Single Sign On servlet starting (Kerberos is enabled in the application). The SSO works in combination with Internet Explorer 10 (a Kerberos login promt pops up), but does not work with Internet Expolorer 9 and 8 and FireFox (Mendix redirect to the basic login form). The Service console logs the following error: Kerberos error: invalid token Negotiate (GSSHeader did not find the right tag), falling back to alternative authentication mechanism. According to the manual this is related to an error in the browser configuration (Kerberos is not enabled and the browser did use an old fashioned NTLM token). However, we have prepared the browsers for Single Sing On conform the instructions of the Kerberos App from the App Store (for I.E.: integrated windows authentication turned on, for FireFox the network.negotiate-auth properties are set). Does anyone know why the Single Sign On service is not working for the browsers IE 9, IE 8 and FireFox?