My b2evolution Version: 1.10.x

Just got a weird error:
============
MySQL error!

Duplicate entry '202042' for key 1(Errno=1062)

Your query:

INSERT INTO evo_sessions( sess_key, sess_lastseen, sess_ipaddress )

VALUES (
'klOdG8UaLcRWj8fYUfeyzOQ6kG8O0cFw',
'2008-04-24 08:47:15',
'118.90.50.249'
)

=============
This blocked access to the site. So I went into PHPMyadmin, found the evo_sessions table, and delteed that record 202042. Incidentally, the record in the db had a different set of data, including IP address, to what was above. Why should b2evo try to double up on session records?
B2Evo v2.41
TIA :?: