The mod was probably installed with multihack( a automated mod plugin)
I would suspect your issues are due to newer versions of perl not supported by your classic version.
I know this sounds like a broken record.
But you should upgrade.
EOL for classic was many years ago and the newer threads versions have uploads built in, as well as many other security patches ,bug fixes and enhancements.
Even though it is version 6.7.1 I believe it will work to jump to threads without first upgrading to classic 6.7.3. And even though the board does not work since the data is all text files. The import should work also.
Now keeping old uploads may be a issue in the upgrade process.
