Fix pack installation fails with error "This tree does not exist"

Package installation of a product fix pack (Hotfix, Feature Pack, Cumulative Fix Pack or Service Pack) fails with the error below.

org.apache.jackrabbit.vault.packaging.PackageException: java.lang.IllegalStateException: This tree does not exist

Cause

The user installing the package is not the "admin" user.

Resolution

To install fix packs, you must be logged in as the actual user with user ID "admin".  Log in as admin user and try again.