Hello,
that's unfortunate, could you please prior an unistallation generate a support package and open a support ticket for this, so we can analyze the issue?
The other options to uninstall the SecureLine are
1) Close the application from the menu bar icon or Dock (so the icon disappears) and drag the Application to trash
2) In terminal execute command: sudo /Library/Application\ Support/AvastSecureLine/hub/uninstall.sh
Best Regards,
Martin