I am behind a corporate firewall, so I install all external modules manually.
While creating a job, the External modules popup told me that I was missing a few jars.
The first one was jboss-serialization.jar, so I downloaded it, unzipped it and installed it manually.
Then when I tried to run my job the external modules screen told me that I needed trove.jar
I downloaded and tried installing various versions of trove.jar from various repositories on the net.
None of them worked. The external Modules screen was still telling me to install trove.jar.
Then I went back to the local disk subdirectory where I had unzipped jboss-serialization.jar and noticed (at last) that there was a second jar hiding in there, called (yes, you guessed it) trove.jar.
I installed that version manually and my problem went away.
Clearly, there is something special about the version which arrives inside the same zip file as jboss-serialization.jar.
Thanks for sharing your case about the hidden jar files with us on forum.