This error generally means that fader (primary or secondary) is not properly connected to the 3420 through its digital base band cable in the back.
DBB cables are only used on A304 or A604 platforms.
1. Verify that your DBB cables are connected properly. Consult the A304 Rack setup guide by starting Test Manager and selecting Help-> Platforms -> A304 -> Rack Setup Guide
2. If your system is hardware wise arranged as a different platform (e.g. A100, A200, A300 ...) make sure that you select the proper corresponding platform when starting your test
The above screen shot shows the dialog that appears when starting to execute a test. The platform selection field shows the A100 platform selected. In that example, the hardware is assumed to be arranged as an A100.
Note that when multiple platforms software installs have been installed with the Radio Access software, multiple platforms can be selected in the dialog. Choose the platform selection that matches your hardware setup