Hey Rush,
This sounds like a coincidence to me, I checked the 1960A data sheet before replying above that does indeed give you 4 Ohms, so if everything else was set to 4 ohms there is nothing that could go wrong.
Do you want to go through some debugging steps? What stopped working the amp or your attenuator? I guess you are using a Power Station?
Check out the “no sound” section of this guide, Power Station: Troubleshooting Guide
Regards,
Dan