Its a macro error "BASIC runtime error.
An exception occurred
Type: com.sun.star.container.NoSuchElementException’
There are different versions of CT2N.
The AOO repository still provivides a version of 2010-09-27 on top.
https://extensions.libreoffice.org/extensions/ct2n-convert-text-to-number-and-dates has version of 2016-08-13.
Which version do you use? Under what version of LibO? For what language(s)?
(I don’t use this extension, but helpers knowing more about it will also need relevant information.)