If you haven't yet got this type of numerical error, you may on day ! Especially if you intend to have Smath do something for you [likely]. Get used to Smath error report, as good as Mathcad/Mathsoft.
Latest versions are more exhaustive in the error description; I get a "Data - not defined"... looking at the code I see there is a uppercase typo in the definition of X.
If you like my plugins please consider to support the program buying a license; for personal contributions to me: paypal.me/dcprojects