I was following the instructions for importing files from mac to rock music library here: https://kb.roonlabs.com/ROCK:_Importing_Music . But in the last step, when I try to open the usb drive directly connected to my nuc (rock), it gives me the following error:
Was that drive on your mac previously? If so, was it formatted as HFS+? Plug it back into your Mac and check. Remember to disable the storage location first, I always find it good practice when moving the external USB to and from the NUC.
If this is the issue, then you will need to reformat that drive in exFAT format. Remember to back up all your music off that drive first. Or, you can just move the drive back to the MAC to add new music and then back to the Nuc.