1) PPA upgrade to 11.5 fails with error:
[ERROR]: Failed to download file: http://autoinstall.plesk.com/PPA_11.5.0/updates/UPDATE_04/POA/upgrade/update.udl2: [Errno 14] HTTP Error 404: Not Found [ERROR]: See update log file /usr/local/ppa/log/ppaupdate.log for details.
2) When PPA tries to install a package with yum, yum complains that the URLs for repositories are not found, and throws 404 errors, as shown above.
Metadata downloaded by yum has become obsolete.
Rename /var/cache/ppa and execute upgrade process again.