You will need to provide further details.
It's worth if you check those logs (if you are based on linux: /var/log/jenkins/jenkins.log but it could be somewhere else)
On the other hand, if you use any ldap authentication within Jenkins you could edit your JENKINS_HOME/config.xml and remove that ldap setup manually (keep a backup file in case you need to rollback).
Regarding the unknown upgrade, that's really weird....
Cheers