First thing: Look on your computer at all of the .wlk file names. If there is a "strange" .wlk file name, then (after stopping WeatherLink) delete that file (feel free to save it somewhere). Restart WeatherLink to see if the problem has been fixed. [Strange would be having the YYYY-MM.wlk have a year or month in the future, or before you had the station, or ....]
Next, if any of the .wlk files have strange sizes, stop Weatherlink, delete them, and restart WeatherLink. [Strange would be REALLY small (other than the most current one), or REALLY big in comparison to the other ones. They will be of varying sizes, of course]
If still not fixed, delete the latest .wlk file (stop, delete, restart). [Currently, 2017-09.wlk]
If still not fixed, delete the files "DataSets.dat" & "DataLists.dat" (stop, delete, restart). [WeatherLink will re-create them on restart]
If still not fixed, you'll probably lose all of your archived data, but create a new station and see if that works going forward.
If not, UNINSTALL and then reinstall WeatherLink.
Let us know which of these steps worked, please.