I started a discussion on this earlier today, when I mistakenly thought that I had downloaded Spark 2.5.8 for customization. I realized later that I actually had 2.6.0.
If I build the source code ("ant release" from the build directory) and either compile with install4j OR simply run startup.bat (from target\build\bin), I can login, chat, and do all normal activities - except for registering a new account. Message is "registering with MYDOMAIN.COM, please wait..." - this never goes away. I have made zero edits to the source - this happens with a freshly checkout out version from SVN.
If I download the already compiled Spark 2.5.8, this issue does not occur.
Server is Openfire 3.7.0 running CentOS 5, standard install. Client environment is windows, issue occurs on both Win XP and Win 7.