From version 15.7.1 onwards, ExpressConnect for Oracle (ECO) does not include Oracle client libraries, which are required to run it. The libraries now need to be downloaded and installed separately.
See the General Information and Technical Notes section of the ECO cover letter for information on correct version and platform of Oracle client libraries, and installation instructions. If the cover letter is not available, see Oracle Instant Client Libraries Installation Instructions in the ExpressConnect for Oracle Installation and Configuration Guide.