下載最新版本無這個錯誤，已經修正、  此前下載的，或者目前存在刪除錯誤的請下載最新的安裝包，或者按以下修改
查找require/msg.php

function delete_msgc($ids = null) {
.............
}
// ..........為省略

把整個函數替換成

function delete_msgc($ids = null) {
        $GLOBALS['db']->update("DELETE pw_msgc FROM pw_msgc LEFT JOIN pw_msg ON pw_msgc.mid= pw_msg.mid LEFT JOIN pw_msglog ON pw_msgc.mid= pw_msglog.mid WHERE pw_msg.mid is NULL AND pw_msglog.mid is NULL".($ids ? " AND pw_msgc.mid IN($ids)" : ''));
}

或者用附件直接覆蓋
原因是，Mysql版本太低的話，導致SQL執行出錯。Mysql5.X以上不會出現此錯誤。

如還沒有解決，請按下面說明處理：
require/msg.php

$GLOBALS['db']->update("DELETE mc FROM pw_msgc mc LEFT JOIN pw_msg m ON mc.mid=m.mid LEFT JOIN pw_msglog ml ON mc.mid=ml.mid WHERE m.mid is NULL AND ml.mid is NULL".($ids ? " AND mc.mid IN($ids)" : ''));

替換成：
MYSQL 4.0.x版本

$GLOBALS['db']->update("DELETE pw_msgc FROM pw_msgc mc LEFT JOIN pw_msg m ON mc.mid=m.mid LEFT JOIN pw_msglog ml ON mc.mid=ml.mid WHERE m.mid is NULL AND ml.mid is NULL".($ids ? " AND mc.mid IN($ids)" : ''));

MYSQL 3.x版本

    global $db;
    $mids = '';
    $query = $db->query("SELECT mc.mid FROM pw_msgc mc LEFT JOIN pw_msg m ON mc.mid=m.mid LEFT JOIN pw_msglog ml ON mc.mid=ml.mid WHERE m.mid is NULL AND ml.mid is NULL".($ids ? " AND mc.mid IN($ids)" : ''));
    while ($rt = $db->fetch_array($query)) {
        $mids .= ($mids ? ',' : '').$rt['mid'];
    }
    if ($mids) {
        $db->update("DELETE FROM pw_msgc WHERE mid IN($mids)");
    }
附件：require_msg.zip