The current WordPress beta does not have the dbconnect() function in the b2functions file, which causes the b2archives.php to fail.
Fix: copy the old b2 function over:
function dbconnect() {
global $connexion, $server, $loginsql, $passsql, $base;
$connexion = mysql_connect($server,$loginsql,$passsql) or die("Can't connect to the database server. MySQL said:
".mysql_error());
$connexionbase = mysql_select_db("$base") or die("Can't connect to the database $base. MySQL said:
".mysql_error());
return(($connexion && $connexionbase));
}