When pre-compiling the schematron rules files. Errors such as xslt-compilation errors, includes not found etc. are always caught and presented with an error message saying incorrectly that the schematron rules file could not be found.
In the two errors above the file has been found but compilation of it has failed.
To make troubleshooting easier i think that a more fine grained error handling could provide the user with a better view of what the underlying error really is.