Group Collection type is mismatched between openymsg and openfire
Several times, the group information of Yahoo! Messenger is lost. After checked, I found there is an exception "java.util.Collections$UnmodifiableSet cannot be cast to java.util.List" which is caused by the mismatched types between openfire (List<String> and openymsg(Set<String>).
ALL (JRE 18.104.22.168)
Do you have a copy of the full stack trace from your logs perchance? I haven't seen this in my own install but that doesn't mean anything. =)