This problem occurs when you run AV UI version 1.0.659.
- Avast Passwords can be edited using the browser extension.
- Click on the Passwords icon at the top-right of your browser. Next, move the mouse cursor to the Passwords entry you want and click "Details". Next, click on "Edit".
Hope that you have fix this issue now, If you want more detailed solution check out my blog here Avast Antivirus not opening.