Thinking that the disk has finally given up the ghost (it was on old PATA hard disk after all), I reconnected the hard disk to my Windows PC, and lo and behold, it worked OK! The same thing happened when I connected the hard disk to my Linux PC - everything worked fine.
This set me off to thinking that the problem lies with the Mac, and after doing a bit of research on the web, discovered that I was not the only one facing the same problem. After wading through all the post on this problem in the various Mac related forums (including Apple's own Support Communities) and trying out the various suggestions given there, I came away baffled. I am not sure why, but Mac's Disk Utility ALWAYS displays the "Unable to write to the last block of the device" message with an uninitialized (blank) hard disk, whether it really is unable to write to the disk or not.
In desperation, I removed the hard disk from the USB enclosure in order to eliminate it's USB interface as the source of the problem. Now I was faced with the problem of connecting the disk to the computer, which do not have any PATA (or IDE) interface. Using a HD dock was out of the question since all docks have SATA interface. I suddenly remembered that I have an adapter that allows me to connect a PATA 3.5" disk, a PATA 2.5" (notebook) disk as well as a SATA disk to a computer via a USB connection. It's kind of difficult to determine who manufactured this adapter since I lost all documentations on the item years ago, but as event proved, the adapter proved to be a life-saver.
The photograph shown below shows the adapter - note that it consists of 2 main parts - the power brick for supplying power to the hard disk and the adapter itself. The adapter has a USB cable attached to it while each long side has the IDE connectors. A SATA connector is present on the top of the adapter. The photo below that shows the adapter fitted on the hard disk prior to testing. All in all, it is a fairly simple device.
Using the adapter, I proceeded to connect the hard disk to my Mac, which popped up a message saying that the disk requires initialization. The Disk Utility was launched and I used this to create a single Mac OS Extended partition. This time it completed the task successfully and I now possess a 500GB hard disk for use with Mac's Time Machine as backup.
Thinking that the original problem lies with the enclosure's USB interface, I proceeded to fit the hard disk back into the enclosure and connected it to the Mac. I was sure that it would fail, but to my surprise the disk performed flawlessly - I could read and write to it without causing any errors. I am now not so sure that the original problem lies with the USB interface and I am still puzzled about the cause of the problem. Any of my blog readers face the same problem? Any feedback would be appreciated.