pain in the proverbial. and rising software was no help. this is how i got it to work:

1) i removed the old firebird installation with this script:

#!/bin/sh
echo “Clean Services”
echo “Clean User”
dscl localhost -delete /Local/Default/Users/firebird
echo “Clean Group”
dscl localhost -delete /Local/Default/Groups/firebird
if [ -f “/Library/StartupItems/Firebird” ]; then
echo “Remove SuperServer StartupItem”
rm -fr /Library/StartupItems/Firebird
fi
if [ -f “/Library/LaunchDaemons/org.firebird.gds.plist” ]; then
echo “Remove Launchd”
launchctl unload /Library/LaunchDaemons/org.firebird.gds.plist
rm /Library/LaunchDaemons/org.firebird.gds.plist
fi
echo “Remove Framework”
rm -fr /Library/Frameworks/Firebird.framework
echo “Remove Receipt”
rm -fr /Library/Receipts/Firebird*.pkg

2) i downloaded FirebirdCS-2.5.0-26074-i386.pkg.zip from sourceforge (this version is intel compatible)
3) i downloaded db_upgrade_mac_V53.zip from auralia website
4) i downloaded setup_server_mac_V53.zip from auralia website
5) i downloaded auralia_m_4.0.5.19_update.zip from auralia website.
6) i ran the Firebird installation tool.
7) i ran the setup_server installation tool, then followed instructions on p14 of the quick start guide to set permissions
8) i edited aliases.conf to point to the new db
9) i stopped and re-started the firebird server with:
launchctl unload /Library/LaunchDaemons/org.firebird.gds.plist
launchctl load /Library/LaunchDaemons/org.firebird.gds.plist

10) i upgraded the database with db_upgrade_mac. it told me my database was up to date.
11) i installed auralia 4 from CD
12) i upgraded to 4.0.5
13) auralia now connects correctly, and on first doing, upgrades the database.
success.

the error seems to be due to the shipped versions of firebird being incompatible with intel based macs.