Trying to add JDBC driver: ... - Error, not in CLASSPATH?

WEKA's default setup for databases tries to locate some common JDBC driver classes ("JDBC" is the Java way of connecting to databases, like MySQL, HSQLDB, etc.) at startup time. By just adding these JDBC drivers to your CLASSPATH, WEKA will be automatically able to connect to these databases. If you are not trying to access a database, just forget about these messages. Otherwise, check out the databases article for more information (the database type that you are trying to connect to might not be listed by default).