Log4j error in java action (java.lang.NoClassDefFoundError: org/apache/logging/log4j/LogManager)

I am having a java action for which I use org.apache library.  Everything worked fine, I ran the same methond on my local env till today. But now, I suddenly happen to have this, for a code sample I did not touch at all.  
1 answers

Go to your app’s directory on your local drive, go to /userlib and remove (or store somewhere else) each jar-file of which there also exists a similar jar-file but with a higher version number. Only keep the ones having the highest version number.

once done, go back to Studio Pro, click F4, then F5, see what happens.