Hi @RaulPerez,
could you please quick check which java version is actual installed on the server by running the following command?
java -version
it might be that you have stumbled over the java issue here: Java update 8u242 breaks execution with RMI executors
I assume that you are using either KNIME server version 4.7 or 4.8 with executor version 3.6.2? Than I would suggest to update your server to a more recent version like 4.10. If you are already on version 4.8 you can also update the server to 4.8.4.
All downloads and update guides are linked here: https://www.knime.com/knimecom-product-downloads
Best regards,
Michael