Plesk upgrade failed with error while upgrading from 11.0.9 to 11.5.30:
'MSI: Error! The older version of Parallels Panel upgrade assistant cannot be removed'
Installing packages upgrading Upgrade Assistant... MSI: Error! The older version of Parallels Panel upgrade assistant cannot be removed. Contact your technical support group. Failed to install 'C:\ParallelsInstaller\parallels\PANEL-WIN_11.5.30\dist-msi-Microsoft-2003-i386\upgrade-assist.msi': Fatal error during installation. (Error code 1603) Error: The installation of the package 'upgrade-assist' failed with code 1603. (upgrade: upgrading Upgrade Assistant...) Not all packages were installed. Please, contact product technical support.
The Plesk autoinstaller had been configured to use custom mirror which does not have upgrade-assist.msi file.
upgrade-assist.msi is missing from Plesk installer packages of current version.
For example, if you are trying to upgrade from Plesk Panel 11.0.9 to Plesk 11.5.30, upgrade-assist.msi (or other packages in error) is missing from
Make sure that all directories in
C:\ParallelsInstaller\parallels\PANEL-WIN_* contain the msi package
If some directory does not have
upgrade-assist.msi package of the same version you can get it from http://autoinstall-win.pp.parallels.com and proceed to upgrade the Plesk.