system
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It has nothing to do with the Avast UI not opening.
If you are using Windows 8.1 adn your Avast was older than 2014.9.0.2008 then its purpose was to update Avast to that version in order to comply with a Microsoft requirement. If you are using Windows 7 or XP it did not result in any changes that I am aware of, and both the registry entry and the emupdate file it referred to could be removed without issue.