You didn't provide any details for us to really understand your problem. Please provide a Short, Self-Contained, Correct Example. It certainly would also help to know more about this "Oracle patching". From what version to what version did you upgrade? What are the relevant changes/releasenotes? Any documented incompatibilities with older clients? Changes to security settings? Deprecated features?

On first glance, this sounds more like a database problem than a Perl problem.

Just in case, try to reinstall the Oracle client libraries and DBD::Oracle. There might be an API/ABI mismatch that prevents a proper connection. Does your command line client (running under the same OS user) work with the same login information?