It's what choroba said: because you're using require instead of use, the module's import method is not called, which is required for the module to work correctly.

$data = IO::All::io() Results in a different error.

That's because there is no sub io anywhere in the distribution. io is dynamically generated by the aforementioned import in the caller's package. The unusual error comes from the fact that the call gets sent to IO::All::AUTOLOAD(), which doesn't handle io.

You need to say either use IO::All; or require IO::All; IO::All->import(); for the module to work correctly.