Third-party implementations of QQ seem to break every so often. Probably intentional on the part of Tencent. The most recent breakage happened around the beginning of june.  The symptom is this message showing up in Help/Debug Window:

Wrong password, server msg in UTF8: 尊敬的用户，您的QQ版本已经停止使用，

请到http://im.qq.com/qq/dlqq.shtml

下载并安装最新的QQ版本。

给您带来不便，敬请谅解！

The suggestion to change the value of QQ_CLIENT to 0x0E1B appears to work.