Occasionally I’ve had reports of an “Invalid property value” error. In recent versions, this might be accompanied by a note about the error occurring “sometime after line 7783”, a message I planted in there deliberately to track down such errors!
Recently, I found and corrected a bug which very occasionally could yield a similar message, but the error in that case was “overflow” and/or “division by zero”. However, I think somebody said they were still seeing the invalid property value.
Well, I just delivered files to a new customer last night, and he had the error on the first attempted run (a manual forecast)! 
In a way, that was good news, though, because he sent me all the relevant files and I wqs able to reproduce the error and track down the cause.
Specifically, in his case, the tirgger was running the forecast just after midnight. There are technical reasons why this isn’t a good idea (and I think I have it prevented in auto run). However, the problem appeared like it could possibly result from other situations, most liekly involving forecasts made before about 10 AM. It involves the reading of localcal.txt, which happens if you have imported local data from your weather station software. It may also depend on just what data types you’re importing.
In any case, I think I have a fix for all of these. If you’ve been seeing the problem, please give this trial version a shot. I’m also curious as to whether the problem was really confined to forecasts made during the monring hours.
This download is a bit different from the other “betas”. This file is NOT the installer. it’s simply a new version of the main executable. What you need to do is download it and save it to c:\wxsim, allowing it to overwrite the 12.8.8 version you may already have.
The URL for this wxsim.exe file is:
Let me know how this goes! 
Tom