This happens probably because Gradle uses commons-io 1.4 and the DITA-OT Gradle Plugin uses a newer version, the classloader randomly picks which version is used, and throws the IllegalAccessError because the FilenameUtils.isSystemWindows is private in 1.4.
A full example stack trace.
This happens probably because Gradle uses commons-io 1.4 and the DITA-OT Gradle Plugin uses a newer version, the classloader randomly picks which version is used, and throws the IllegalAccessError because the
FilenameUtils.isSystemWindows
is private in 1.4.