The OCI version of the Easysoft ODBC-Oracle Driver uses Oracle's client libraries. If you are using the OCI version of the driver with the standard database client, the ORACLE_HOME environment variable needs to be set (and exported) to where you installed Oracle (or the Oracle client). See When do I get error "[EasySoft]ORACLE_HOME not defined Error 69"?
The Easysoft ODBC-Oracle driver distribution includes a program called checksys, which you can run to test everything is set up correctly. You can find checksys in /usr/local/easysoft/oracle. You run checksys like this:
./checksys -d oracle_data_source
where oracle_data_source is the name of your Easysoft ODBC-Oracle Driver data source. checksys can tell you if ORACLE_HOME is set correctly and diagnose many other setup issues.