to help you, tell us which model of nexto you own?

Nexto DI nvs2501

please check if the CF pins are bent, or not.
if so, it needs to be exchanged.
you can contact local distributor to get help.
http://www.nextodi.com/store/nvs_offline_store.html

They are not bent. The Nexto backs up CF cards to itself fine. It will not back up to the external hard drive at the same time. I have to do separate data transfers.

so, you mean,
1. you can copy from CF to the internal HDD of NVS2501.
2. but you can't copy from CF to both internal & external HDD.
3. you can copy from internal HDD to external HDD.

is it right?
if so, the unit seems to be needed repairing.
please contact the seller for RMA.

Best regards

Did you plugged in 12v switching adapter or Nexto external battery(sold separately ) to your NVS2501??