Unable to open domain’s Backup & Restore page in Plesk: Failed to parse response. Error message: > required – Plesk

Symptoms

• It's not possible to access domain's Backup Manager in Plesk with the following error:

  Server Error
  500
  PleskPMMResponseException
  Failed to parse response. Reason: XML error at line 6 column 39. Error message: > required
  Process output:
  <?xml version="1.0" encoding="UTF-8"?> <response> <errcode>0</errcode> <data> <task-list> <task task-id="613" name="" mail-to="" owner-guid="C65DC245-4B9F-4957-B88E-2F5537CA8713" task-type="Backup" task-pid="" owner-type="server" backup-profile-name="" creation-date="" fullname=""> <task-status task-id="613"> <finished status="error" log-location="C:Program Files (x86)PleskPMMsessions<session-id>migration.result"> </finished> </task-status> <dumps-storage-credentials storage-type="local" use-passive-ftp-mode="false" use-ftps="false"> <root-dir>C:Program Files (x86)PleskBackup</root-dir> </dumps-storage-credentials> </task> <task task-id="612" name="backup_info_1812290102.xml" mail-to="" owner-gu
  File PMMConnector.php
  Line 933

• The following errors could be found in the %plesk_dir%adminlogsphp_error.log file:

  DEBUG [util_exec] [5c27e2161c284] Starting: pmmcli --get-tasks-list, stdin:
  DEBUG [util_exec] [5c27e2161c284] Finished in 0.00279s, Error code: TRUE, stdout: , stderr:
  ERR [1] PleskPMMResponseException: Failed to parse response. Reason: XML error at line 6 column 39. Error message: > required Process output: <?xml version="1.0" encoding="UTF-8"?>
  <response>
      <errcode>0</errcode>
      <data>
          <task-list>
              <task task-id="613" name="
  PleskPMMResponseException: Failed to parse response. Reason: XML error at line 6 column 39. Error message: > required Process output: <?xml version="1.0" encoding="UTF-8"?>
  <response>
      <errcode>0</errcode>
      <data>
          <task-list>
              <task task-id="613" name="

• The command below returns the next output in Windows:

  C:> "C:Program Files (x86)Pleskadminbinpmmcli.exe" --get-tasks-list Backup
  <task task-id="613" name="" mail-to="" owner-guid="C65DC245-4B9F-4957-B88E-2F5537CA8713" task-type="Backup" task-pid="" owner-type="server" backup-profile-name="" creation-date="<date>" fullname=" ">
  <task-status task-id="613">
  <finished status="error" log-location="C:Program Files (x86)PleskPMMsessions2018-12-29-040001.890migration.result">
  </finished>
  </task-status>
  <dumps-storage-credentials storage-type="local" use-passive-ftp-mode="false" use-ftps="false">
  <root-dir>C:Program Files (x86)PleskBackup</root-dir>
  </dumps-storage-credentials>
  </task>

OR

• With enabled debug the following records can be found in  /var/log/plesk/panel.log file:

  [2019-09-20 12:45:01] ERR [1] Exception: XML error at line 90 column 32. Error message: > required
  file: /usr/local/psa/admin/plib/StreamXMLReader.php
  line: 115
  code: 0
  trace: #0 /usr/local/psa/admin/plib/StreamXMLReader.php(179): StreamXMLReader->parse()
  #1 /usr/local/psa/admin/plib/StreamXMLReader.php(248): StreamXMLReader->read(string 'task-status', integer '2', integer '1', integer '0')
  #2 /usr/local/psa/admin/plib/backup/protocol/PMMResponseTaskList.php(87): StreamXMLReader->sub(string 'task-status', integer '2')
  #3 /usr/local/psa/admin/plib/backup/protocol/PMMResponseTaskList.php(208): PMMTask->__construct(object of type StreamXMLReader)
  #4 /usr/local…