If you didn't tell me it was a Western Digital brand drive, I would have asked you specifically that as they have been problematic since back in the early 2000's because they seem to draw a lot more power than typical USB provides on spin-up. This can cause them not to start properly or to be mis-read and thus unavailable or provide error messages.
Please try using a Y-cable to provide power from another source, or use a different brand drive and see if you still have the same error.