Can't get instant client to work on Win XP

Question

This is driving me nuts. I'm trying to get instantclient10_1 (10.1.0.4) to work reliably on Win XP so I can use it in deploying a Python app I'm writing. I have one XP system on which I have the instant client installed and working. By this I mean that it works with the appropriate of sqlplus. It also works with cx_Oracle. However, I do need to set ORACLE_HOME in order to achieve this (contra the documentation). I do not seem to need to set SQLPATH.
But I can't get it to work on any other system. I copy my instantclient10_1 directory over and use the same batch file that works on the "good" system, but I get "invalid or unknown NLS parameter value specified". I'm using a command of the form
sqlplus user_name/[email protected]:1521/db_name
I've also tried a "fresh" install on that machine. Same story. I've tried it on another machine as well. Same story. It only works on this one machine!
It actually took me quite a while to get it to work on that machine, involving installing and uninstalling the full client, the instant client, both, etc. But it does work there.
Another odd "feature": On the "good" machine, if I fail to set ORACLE_HOME, it errors and suggests I do this. On the "bad" machine, I just get the "invalid or unknown NLS" error.
There are other ORACLE directories on these machines (e.g., ORA17). But I get the same results if I hide these and take all reference to them out of environment variables.
Any suggestions will be greatly appreciated. Why is it working on the one system? Why isn't it working on the others?

Answer 1

There's one more way that the previously-existing Oracle directories on the other machines might be tripping you up - with registry settings. In particular, the HKEY_LOCAL_MACHINE\SOFTWARE\ORACLE\(some home)NLS_LANG registry key may be associated with the "invalid or unknown NLS parameter value specified" error you're getting.
Of course, the Instant Client isn't supposed to have to mess with the registry, so that makes me suspicious. And I got Instant Client SQL*PLUS on a clean XP machine to work without setting an ORACLE_HOME. All this makes me suspicious that some stuff from outside your Instant Client is being run. I know you said you cleaned your environment variables, but double-check that the other Oracle directories are out of your PATH.
If you have permission to, you might want to thoroughly scrub the old Oracles from the other machines (starting with running the Oracle Installer, then hand-cleaning the registry, the c:\Ora92 or whatever directory, and then c:\Program Files\Oracle). If you have MetaLink, Document 74790.1 is a dated but good guide to cleanly de-installing an old Oracle installation from Windows. It's much more difficult than it ought to be; sometimes it feels like an Oracle home is never truly gone. If you can't do that, perhaps save a copy of your registry and then temporarily rename HKEY_LOCAL_MACHINE\SOFTWARE\ORACLE to ORACLE_HIDDEN, or something - something to keep any existing registry settings from distracting your Instant Client.
Good luck!