Subject Firebird CS 1.5 connect -902 'system could not find the environment option..'
Author fergusatpontem

After installing Classic Server v1.5.2 (and 1.5.3) on a Dell XP SP2
system recently, attempting to connect to a db from isql with the
connect command was giving SQL -902 error followed by
"The system could not find the environment option that was entered"

The TCP/IP LSPs installed in Windows showed one non-standard item:

This belongs to the McAfee Personal Firewall Privacy Service.
Uninstalling it fixed the problem with connecting to Classic Server.

Details on how to uninstall the McAfee Privacy Service are here: