The installation of micro-updates started from the Plesk home screen fails:
Failed to update Panel. You can send the update log to Parallels support to try fixing the issue. View the update log.

Attempting to access the update log fails:

Error Internal error: File specified by 766460e6-7587-54f1-e1be-794e5655c4a4 was not found Message File specified by 766460e6-7587-54f1-e1be-794e5655c4a4 was not found File LogFile.php Line 36 Type Smb_Exception_NotFound

Cause

The Plesk Installer has failed or was terminated.
Workaround

1) (Linux only) Remove the /tmp/psa-installer.lock file

2) Remove stale records from the ‘psa.longtasks’ and ‘psa.longtaskparams’ tables:

mysql -uadmin -p`cat /etc/psa/.psa.shadow`
mysql> use psa;
mysql> begin;
mysql> DELETE longtasks, longtaskparams FROM longtasks INNER JOIN longtaskparams WHERE longtasks.type='panel-update' AND longtaskparams.task_id=longtasks.id;
mysql> commit;

Install updates through Tools & Settings > Updates and Upgrades or from the command-line

# /usr/local/psa/admin/bin/autoinstaller --select-product-id plesk --select-release-current --reinstall-patch --install-component base

If the update fails again, Check you logs:
/tmp/autoinstaller3.log
c:\ParallelsInstaller\autoinstaller3.log