I had a momentary surprise when I realized I didn’t have Paratext 8 on one of my home laptops so I installed it. After the install, Paratext 8 wouldn’t start, it gave a complicated error message about an error in a writing system store. Then I remembered, I’d seen this error reported last month, so I went ahead and downloaded the update patch from paratext.org, ran it and after the update Paratext 8 started with no problems. So if you encounter an error about a writing system after installing Paratext 8 for the first time when 9 was already installed, try downloading the latest update for Paratext 8 to get past it.
