Do you experience problems during downloading?
Check your connection in Status and Interface settings window.
Use Test Server in Config > Servers.
We will probably ask you to do a test using only basic settings.
Do you experience problems during repair or unpacking?
Enable +Debug logging in the Status and Interface settings window and share the relevant parts of the log here using [ code ] sections.
It seems a virusscanner might have broken things. You are probably missing a file.
Just to be sure, you are just using the Standalone version from the Downloads page? Because then you don't need any python and whatever you do in Python doesn't affect SABnzbd since the Standalone version has Python built-in.
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I've been using the standalone versions each upgrade yeah.
I also tested the installer for good measures but with the same results.
Virusscanner didn't complain about the files and downgrading to 3.5.3 made it work again.
But I found my issue: overwriting old files with new ones (never had issue before).
Clean install works fine.
Exact same problem as the OP, Windows Server 2012 R2 and I always just copy the new standalone version over the old but in this case v3.6.0 needed a clean folder to start with