Unable to create a Plesk scheduled backup to a remote FTP storage: Curl error: Unable to resume an interrupted download: (28) Timeout was reached

Symptoms

• In an attempt to create a Plesk scheduled backup to a remote FTP server the process fails with the error:

  PLESK_ERROR: pmm-ras failed (Error code = 1):
  STDOUT: Curl error: Unable to resume an interrupted download: (28) Timeout was reached: Last FTP request: PASS *****: Last FTP response: 421 I can't accept more than 3 connections as the same user: Connection to the FTP server has lost

• The similar or the following error can be found in usr/local/psa/PMM/logs/backup-XX/backup.log file:
  

  CONFIG_TEXT: Curl error: (21) Quote command returned error: Last FTP request: QUIT Last FTP response: 221 Goodbye [common/plesk-utils/PMM/repository-transport/transport.cpp:1010] virtual void plesk::tRepositoryFtp::Delete(const string&) INFO: pmm-ras finished. Exit code: 126

• The following errors can be found in /var/log/plesk/PMM/backup-XX/pmmcli.log and /var/log/plesk/PMM/pmmcli.log files:

  CONFIG_TEXT: [type 'exceptions.TypeError'] cannot concatenate 'str' and 'list' objects
  TypeError: cannot concatenate 'str' and 'list' objects
  [error][module]pmmcli[/module][operation]<type 'exceptions.TypeError'>[/operation][message]cannot concatenate 'str' and 'list' objects at File "/usr/local/psa/admin/sbin/pmmcli", line 6, in <module>

Cause

This is a Plesk bug with the ID #PPPM-8749, which will be fixed in the next Plesk update releases.

Resolution

Until the bug will be fixed, apply the following workaround:

1. Log into Plesk.
2. Go to Extensions > My Extensions > Panel.ini Editor > Open > Editor.
   

   Note: in case the Panel.ini Editor extension is missing, install it using this article.

3. Add the line below under the [pmm] section:
   

   CONFIG_TEXT: ftpForbidReuseConnection = 1

4. Scroll down and press the Save button.