In this case you can enable the server executable in Firewall:
1. Open Avast Free Antivirus.
2. Click Protection.
3. Once the options appear, click Firewall.
4. Click the Gear Icon to open the Firewall Settings.
5. Find What should Avast do with apps that have not been yet assigned application rules or something similar.
6. Near that, select View Application Rules or something similar.
7. Once you get a window select Application Rules.
8. Scroll down and find the FTP application.
9. Edit the firewall rules to ensure Avast always Allows the app.
10. Try it again and see if it fixed your problem.
If this does not work, feel free to contact again.