Firewall will not start on new install

After my prior AV software developed a performance problem the vendor seems unable to fix, I am trying a few others. I had ESET Smart Security working just fine.

In my testing I uninstalled it, rebooted, and installed BitDefender AV. It took way too much memory, and was a bit flaky. So uninstalled this one, with the idea to go back to ESET.

However, now after reinstall, the firewall will not start. Log shows "Personal firewall An error occurred while starting firewall services. The Personal firewall will not work."

I am suspicious that BitDefender has changed something on my system, since ESET worked prior. However, I cannot locate anything specific.

Any ideas?