The error “Could not find or load main class files” could occur when the java couldn’t find the class it’s looking for.
You can check whether the preferred Java Virtual Machine is selected in “Denodo Control Center>Configure>Java Virtual Machine>Edit”
Ensure that the default port(9999) of Virtual DataPort Server is listening and not other application using that port.
For more information about this error, you can check the log file located in <DENODO_HOME>/logs/vdp/vdp.log
You can have a look at [Virtual dataport doesn't start](https://community.denodo.com/answers/question/details?questionId=90670000000CcC8AAK) Community Q&A for more options.
Hope this helps!