There has been an ongoing issue with thread prefixes. System was set to require a prefix when starting a new thread. Some users told me they could not start threads because the prefix pull-down menu did not even appear. Stumped our admin guy. This morning I received a message from someone that said he could see the prefix pull-down menu in only one forum section. That was the clue I needed to fix the problem.
While I was at it, I also set the system to make thread prefixes optional. Still a good idea to use prefixes when you start threads as it makes it easier for people to find the information they are seeking.
If anyone still has issues with prefixes, please let me know.