Forum registration (and by extension site registration) is currently broken. The problem appears to be a bug in how phpBB2 handles session data.
Could not delete stale confirm data
DEBUG MODE
SQL Error : 1153 Got a packet bigger than 'max_allowed_packet' bytes
DELETE FROM confirm WHERE session_id NOT IN ('00001f59ef510e916b1ea86e69301d2a', '00009014266c63e445525630580e9eb0', '00009b5664debb52e5e34cb34d1ba014', (insert another million or so entries))
Line : 1059
File : usercp_register.php
Backtrace:
includes/functions.php[743]: ErrorPrintBacktrace()
includes/usercp_register.php[1059]: message_die(202, <pre class='xdebug-var-dump' dir='ltr'><small>string</small> <font>'Could not delete stale confirm data'</font> <i>(length=35)</i>
</pre>, <pre class='xdebug-var-dump' dir='ltr'><small>string</small> <font>''</font> <i>(length=0)</i>
</pre>, 1059, {string(62)}, {string(32680093)})
profile.php[92]: include({string(62)})
I am posting this to note we are aware of the issue, however this is beyond my ability to easily fix, so it might take a while until a real fix is out.