Sounds like your updates might be out of sync. I recommend going to your Start Menu and Choosing ProSeries 2020 -> Tools Repair Updates.

If your system still is still unable to startup after that, please email [installation directory]\32bit\proseries.txt and [installation directory]\appData\updateLog.txt to proseries_engineering@intuit.com.  If you're not sure how to do that or prefer working with someone, please call into customer support - they have the tools available to them to see what's going on and attempt to remediate.

If you can run ProSeries after that but Email Client Checklist still crashes, please enter "From Fred2020" in the crash dialog, along with what email client is your default.  if it's something like Thunderbird 64 bit, go into Tools -> Options -> General and select "64 bit email client". Then try again.