How have you gone about the upgrade? Ie. Was the 1.5.3 database taken to another location/server where the php version is/was different than the final location? Have you tried using the password "reset" sql once the 1.5.3 database was in position to upgrade to 1.5.4? Are you using credentials that exist and work in the 1.5.3 version of the database? The fix referenced above was to support upgrading TO 1.5.3 not from it.
Reset password SQL: http://www.zen-cart.com/content.php?44
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