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The functionality makes use of functions from "mcrypt" extension of PHP, which by default are not available on every server. Without extension being present any attempt to use it's functions would end up in Fatal Error. Since we're using it for session cookie encryption no session can be established and user won't be able to login to Admin Console or Installation Wizard to fix things.
Solution
Require "mcrypt" extension to be present on the "System Requirements" step during In-Portal installation/upgrade.
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