Hi NucleusVM,
I have exactly the same USB HDD (18a5:0237 Verbatim, Ltd Portable Harddrive (500 GB)) connected to ESXi 5.5 (Update 2) and I suffer with exactly the same problem as you :-(
I've tried a lot of things that I found in the internet but nothing helps. Any idea anyone? Isn't this particular USB HDD compatible with ESXi? Any hints anyone?
BR, Kulich78