the ORACLE_HOME is defined in the windows registryWhy do you have a separate Oracle install/home, while trying to use Instant client on the same machine? Can you not just use sqlplus from the existing home?
the program may be searching sqlnet.ora which it is
pointing to use tnsnames. I need to remove this fileTo override sqlnet.ora settings you should be able to use your own sqlnet.ora in the Instant client directory, e.g. with a single line with names.directory_path=(ezconnect).
to test whether this works without the sqlnet.ora but