Are you on a case-sensitive file system?

The file system (and Perl) make a distinction between

Sys::RunALone  # upper case "L"
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and

Sys::RunAlone  # lower case "l"
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Once you fix that in your script, you'll find that error gone.

You could also have found that yourself from the error message:

Can't locate Sys/RunALone.pm in @INC (...)
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If you search for the file RunALone.pm, you will find that in fact it is not there, which should have told you that there is a subtle difference in what you ask for and what actually exists.