I use linux, I found version 3.5.1 on my disk, because I did not deleted it after update:). Removing old version is just an “rpm -e openfire”. Just make sure to backup configuration (*xml files somewhere in /opt/openfire dir). I do not know anything about windows.
If reverting fixed the issue (maybe just temp), then I would suspect that the database has an issue. maybe you upgrade did not fully convert the database. If you are using LDAP and an external database I would run the database upgrade scripts again. If that does not fix it start with a clean database after running a backup of the current one.
I know this is an old post, but wanted to add to the discussion in case it helps someone else…
I had this same issue where I could not login to the admin console after a restart. The only way was by changing the config file, setting the stup flag to false and then going through the install steps again. By the way, I was running openfire on a Microsoft Windows 2008 R2 server, with SQL Server 2008 as its database and Active Directory for authentication…
Now what tripped me over was that I was using Windows authentication for the database access! The issue went away by simply using a SQL Login. Also mentioned here:http://community.igniterealtime.org/thread/40665
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Regards