Major Expired Novell accounts. When this happens, Sakai (we are currently running version 10.7) doesn't seem to know how to handle it - it gives the user an error screen, and shows the following sort of thing in the logs:
2017-01-06 10:54:06,275 WARN http-bio-8080-exec-3 org.sakaiproject.portal.util.ErrorReporter - Bug Report bug-id: 60678a65-bd79-4a56-bda3-e63df6d743e3 user: null usage-session: null time: Jan 6, 2017 10:54:06 user comment: null stack trace org.sakaiproject.portal.api.PortalHandlerException: java.lang.RuntimeException: authenticateUser(): LDAPException during authentication attempt [userLogin = sititus][result code = Unwilling To Perform][error message = NDS error: log account expired (-220)] at org.sakaiproject.portal.charon.handlers.XLoginHandler.doPost(XLoginHandler.java:50) caused by: java.lang.RuntimeException: authenticateUser(): LDAPException during authentication attempt [userLogin = sititus][result code = Unwilling To Perform][error message = NDS error: log account expired (-220)] at org.sakaiproject.user.impl.BaseUserDirectoryService.getProviderAuthenticatedUser(BaseUserDirectoryService.java:1690) caused by: LDAPException: Unwilling To Perform (53) Unwilling To Perform LDAPException: Server Message: NDS error: log account expired (-220) LDAPException: Matched DN: at com.novell.ldap.LDAPResponse.getResultException(LDAPResponse.java:407) at com.novell.ldap.LDAPResponse.chkResultCode(LDAPResponse.java:370) at com.novell.ldap.LDAPConnection.chkResultCode(LDAPConnection.java:3959) at com.novell.ldap.LDAPConnection.bind(LDAPConnection.java:1408) at edu.amc.sakai.user.PooledLDAPConnection.bind(PooledLDAPConnection.java:87)