To my eye, it looks like the Clan ID in the clients cache is wrong. (seriously wrong) But that's just what it looks like the server is saying.
We don't know if you are getting many of these log entries, and that is just an example. If this is only happening for one player or lots. If there are other variations, in the clan codes or such.
We don't, actually, know which Clan IDs are valid for your server, but I would certainly suspect that the negative one the server is claiming the client provided is not valid.
Those things will help you build up a better picture.
If every player is providing such an invalid Clan ID, then perhaps your web server is issuing IDs to them in a way they do not read correctly, rather than them being wrong in their local cache, or maybe your web server is not reading the Clan ID they pass back properly.