When connecting to a DB2 database one of the following error messages may appear in the connection message in DbVisualizer:

For DB2 z/OS:

"The IBM Data Server for JDBC and SQLJ license was invalid or was not activated for the DB2 for z/OS subsystem. If you are connecting directly to the data server and using DB2 Connect Unlimited Edition for System z, perform the activation step by running the activation program in the license activation kit. If you are using any other edition of DB2 Connect, obtain the license file, db2jcc_license_cisuz.jar, from the license activation kit, and follow the installation directions to include the license file in the class path."
For QDB2:
"The version of the IBM Universal JDBC driver in use is not licensed for connectivity to QDB2 databases. To connect to this DB2 server, please obtain a licensed copy of the IBM DB2 Universal Driver for JDBC and SQLJ. An appropriate license file db2jcc_license_*.jar for this target platform must be installed to the application classpath. Connectivity to QDB2 databases is enabled by any of the following license files: db2jcc_license_cisuz.jar"

The message is generated by the JDBC driver and has nothing to do with the licensing for DbVisualizer.

What you need to do is open the Tools->Driver Manager in DbVisualizer and add the requested db2jcc_license_*.jar file to the Driver jar Files list for the DB2 or DB2 z/OS driver.

The db2jcc_license_*.jar file is usually included with the DB2 Connect software. 

Read more here: http://www-01.ibm.com/support/docview.wss?uid=swg21191319