I was able to reproduce this problem last night with Avast.. similar might be happening with other anti-virus or anti-malware vendors

For me, after installing Avast it prompted me during an update with something along the lines of "We Just protected your file. ProSeriesUpdater is trying to change the file updateLog.txt in C:\ProWin20\appdata. What would you like to do?" When I clicked "Block App", I started getting those Update Error (18) during updates.

To fix, I had to go into their Ransomeware Shield, check all the ProSeries directories, and click "Stop Protection"

Now, I have no idea why Avast "protected" ProSeries 20 and ProSeries 19 - both write logging information to our own /appdata directories.  We will have to try to find a contact in Avast to dig in.