Right. org.zefer.pd4ml.PD4ML are wrapper classes are included to v4 JAR to translate the older calls to the new API.
Older v4 builds had troubles to find/read pd4ml.lic in some environments – obviously you faced with the problem.
Try the newest JAR to see if it solves the problem or not.
If you do not use pd4ml.lic and pass the license number string via PD4ML v4 API call, you may still access the API even from org.zefer.pd4ml.PD4ML. There is a public field PD4ML.pd4mlNew – a reference to its wrapped com.pd4ml.PD4ML instance