This error is thrown when I launch the Liferay Tomcat server from Eclipse. I have been following this tutorial: https://help.liferay.com/hc/en-us/articles/360029147251-Installing-a-Liferay-Server-in-Dev-Studio
I am posting this Q&A because I lost some time in debugging this silly situation and hope this is helping the others - The reason is because wrong path configured for Tomcat Server when declaring new Server: I have been set the <path_to_liferay_tomcat_bundle>\liferay-ce-portal-7.3.5-ga6 and it should have been <path_to_liferay_tomcat_bundle>\liferay-ce-portal-7.3.5-ga6\tomcat-9.0.37
I was misled by the fact that Eclipse said it recognize the project as being a Tomcat one - the message - "Detected portal bundle type: Tomcat"