If you are getting the below error while updating the Plesk versions or installing the microupdates , have a try with the mentioned solution :

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ERROR: Unable to download the MD5 sum for the new Parallels Installer binary.
Not all packages were installed.
Please, contact product technical support.
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Solution :
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Remove cache from /var/cache/parallels_installer/ and start auto-installer again.
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If you require help, contact SupportPRO Server Admin