What does the message Tracking number has wrong checksum mean?

That message means that the track number of the shipment did not match to UPU S10 standard, all the track number (identifiers) of international parcels and mails should correspond to it.

There is a possibility that the track is wrong or false.

However, the track may be tracked normally. But you should give a maximum attention to parcel with such track, at least, until first event for track.