I just recieved the exact same error message when trying to connect to our KNIME Server. License files are valid and should also be in the correct folder. I also restarted the database using asadmin to ensure everthing is running correctly. However, the problem remains.
According to the server.log, the problem is caused by an EJBException. I've attached the corresponding server.log snippet.
If required, I can also provide the complete log file.
Please create a file <server-repository>/workflows/.metainfo/repositoryVersion with "3.8.0" as contents. This is a problem with fresh installations of 3.8.0.