You just need to get a / the latest copy of the XSLT library and put it there.
A word of caution for advanced users UPDATING the XSLT-Library…
The fmCheckMate XSLT library has no complicated install process, which means
IF you plan on changing the XSLT functions,
or writing your own, you should create your own library
by renaming the fmCheckMate.YOUR_NAME_HERE folder
and putting your edited files there.
Like that you avoid overwriting your changes when you update the library!
For exampe, I've got my own "fmCheckMate.mrwatson.de" library.
This works, because fmCheckMate looks in all folders that begin with fmCheckMate.
How to install fmCheckMate XSLT on a Mac