MyBook Essential 2TB suddenly refuses to write -- still reads just fine

For no known reason, my USB 2.0 MyBook Essential 2TB running under Windows 7 Pro SP1 has stopped being writeable. I can still read without difficulty, but any attempt to write to the drive generates the Windows message “cannot read from source.”

I realize that the message suggests that the problem is from the source drive and not the MyBook, but I have no difficulty writing to/from any of the other drives in my system. The MyBook also fails the SmartWare Quick and Complete drive tests (with no additional error messages beyond ‘fail’).

I have tried other USB cables and checked the power supply – no obvious problems. I have tried several repowers as well as Windows’ disk checking utility.

I am now backing up all the data to the other drives on my system (and a few smaller capacity externals I have lying around) preparatory to downloading the latest firmware (if that works) and then reformatting (if that works).

Any other suggestions? TIA.

My suggestion would be to replace the whole drive since it failed the diagnostics made to test that specific drive…