I'm trying to get a Single Sign On system working, but I keep on hitting the same error. Here is a part of the logs: Code: [Tue Dec 27 14:34:23 2011] [debug] src/mod_auth_kerb.c(1667): [client 10.29.0.153] kerb_authenticate_user entered with user (NULL) and auth_type Kerberos [Tue Dec 27 14:34:23 2011] [debug] src/mod_auth_kerb.c(1667): [client 10.29.0.153] kerb_authenticate_user entered with user (NULL) and auth_type Kerberos [Tue Dec 27 14:34:23 2011] [debug] src/mod_auth_kerb.c(1277): [client 10.29.0.153] Acquiring creds for HTTP/[email protected] [Tue Dec 27 14:34:23 2011] [debug] src/mod_auth_kerb.c(1424): [client 10.29.0.153] Verifying client data using KRB5 GSS-API [Tue Dec 27 14:34:23 2011] [debug] src/mod_auth_kerb.c(1440): [client 10.29.0.153] Client didn't delegate us their credential [Tue Dec 27 14:34:23 2011] [debug] src/mod_auth_kerb.c(1468): [client 10.29.0.153] Warning: received token seems to be NTLM, which isn't supported by the Kerberos module. Check your IE configuration. [Tue Dec 27 14:34:23 2011] [debug] src/mod_auth_kerb.c(1138): [client 10.29.0.153] GSS-API major_status:00090000, minor_status:00000000 [Tue Dec 27 14:34:23 2011] [error] [client 10.29.0.153] gss_accept_sec_context() failed: Invalid token was supplied (, No error) login via basic auth Code: [Tue Dec 27 14:34:31 2011] [debug] src/mod_auth_kerb.c(1667): [client 10.29.0.153] kerb_authenticate_user entered with user (NULL) and auth_type Kerberos [Tue Dec 27 14:34:31 2011] [debug] src/mod_auth_kerb.c(1025): [client 10.29.0.153] Using HTTP/[email protected] as server principal for password verification [Tue Dec 27 14:34:31 2011] [debug] src/mod_auth_kerb.c(714): [client 10.29.0.153] Trying to get TGT for user [email protected] [Tue Dec 27 14:34:31 2011] [debug] src/mod_auth_kerb.c(1110): [client 10.29.0.153] kerb_authenticate_user_krb5pwd ret=0 [email protected] authtype=Basic [Tue Dec 27 14:34:31 2011] [debug] src/mod_auth_kerb.c(1667): [client 10.29.0.153] kerb_authenticate_user entered with user (NULL) and auth_type Kerberos [Tue Dec 27 14:34:31 2011] [debug] src/mod_auth_kerb.c(1605): [client 10.29.0.153] matched previous auth request my krdb5 config file: Code: [logging] default = FILE:/var/log/krb5libs.log kdc = FILE:/var/log/krb5kdc.log admin_server = FILE:/var/log/kadmind.log [libdefaults] default_realm = PREDIKA.BE dns_lookup_realm = false dns_lookup_kdc = false ticket_lifetime = 24h renew_lifetime = 7d forwardable = true [realms] PREDIKA.BE = { kdc = PREDIKA.BE } [domain_realm] .predika.be = PREDIKA.BE predika.be = PREDIKA.BE [logging] kdc = FILE:/var/log/kerberos/krb5kdc.log admin_server = FILE:/var/log/kerberos/kadmin.log default = FILE:/var/log/kerberos/krb5lib.log the apache config: Code: <IfModule mod_auth_kerb.c> AuthType Kerberos AuthName "Kerberos Login" KrbMethodNegotiate on KrbVerifyKDC off KrbSaveCredentials off KrbMethodK5Passwd on KrbServiceName HTTP/[email protected] KrbAuthRealms PREDIKA.BE Krb5Keytab /etc/krb5.keytab require valid-user </IfModule> I'm totally confused. Maybe someone has seen the problem before, or can see an error in my configuration?