Your adapter can't handle two simultaneous connections!
True, haha. I learned this lesson a while back when I first got into Arduino. I have double-checked to make sure that only a single terminal program is running and accessing the COM port of the USB dongle.
What exactly happens when you access the adapter from your Serial Terminal? Does the adapter respond to any commands when the nrf24l01+ is unplugged? (My adapter doesn't but they might be different...)
I tried that and I don't get any errors. My guess is that the adapter is working in that it accepts data from the PC. But without any loopback or receiver, I obviously won't get anything back. If I plug the nrf back into the USB dongle, then I get the same error again.
Try the adapter with the low power version of the nrf24l01+ module. For me the amplified version worked well but that doesn't guarantee that yours will as well. The modules seem to be hit or miss since even some of my low power ones don't work with the adapter.
I only have the two that I ordered from Makerfocus, but I'll procure some other brands today to see how it goes.