Unsupported File System when reconnecting USB exn2

My 2tb wd elements was recognized just fine at first. I unplugged it from the NAS, hooked it up to my laptop and copied 100gb of data to it. I then hooked it back up to the NAS and received the error:

Unsupported File System
An unsupported file system has been detected on a USB device (vendor Western_Digital, model: Ext_HDD_1021, serial number: ------, file system: N/A, label: N/A). Please remove the USB device.

It can’t be the file format since it worked fine an hour earlier and all that I did was connect it to my laptop to copy over additional files. Anyone know how to fix?

If anyone is interested I was able to resolve the issue by connecting the USB drive to my laptop, running the Windows disk error check utility, clicking “safely eject usb device” in the systray and reconnecting it to my NAS. I think disconnecting it without safely ejecting caused lost/corrupted background files that windows ignores, but trips the NAS OS up.

What format is the 2 TB Elements USB drive? exFAT? NTFS? HSF+??

It’s NTFS.