If you have a use line for Crypt::PasswdMD5, and it's not installed, things should die right there.

If you have a require line for Crypt::PasswdMD, and your program makes it past that OK, that also proves that you have it installed, but you'll still get the error you're getting. In that case, change the "require" to "use" instead.

If your program does not ever "use" or "require" Crypt::PasswdMD5, you need to add that.

use Crypt::PasswdMD5;
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If that doesn't work, I'm guessing you have an installation problem.