USB drive write protected error

Well. I was copying files from my hard disk to a flash drive. In the middle of it, I click the cancel button. After that, I was not able to copy any file to it or delete file from it. I can't even format it.
The message I got is 'write protected'.

I googled for solutions, there are basically two kind of posting:
1. HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\StorageDevicePolicies
2. diskpart

I tried both, but neither one worked.

I did followed the diskpart instruction and was able to play it with a new USB flash drive. The diskpart is basically a text based utility. Once you type the diskpart in the Run or DOS Command window, a terminal like window is popped up and you can issue text commands. Type help and hit enter will show you all the command available. Typing help and a command name will show you how a given command is for and how it is used.

In my USB case, it seems that my USB is dead - I can issue the clear read-only status command and be notified the successful of the command. But when I check status, the read-only status is still set. With my new USB, the diskpart worked like a charm.

Note: There are status for both the 'disk' and 'volume'. You need to check/reset both.

Now - did cancel a copy command killed my USB drive? I don't know. But at this point, I have broken quite few USB drive with no obvious reason - it seems to me it is really un-reliable - worst than the 3.5 inch floppy disk.

I really wondering if there are any statistics about the reliability of the USB drive.

Added on Feb. 5, 2011=============
I actually read some articles about how the USB drive works and a report on the usability of the USB drive. It seems to me that USB drive suppose to be quite reliable - especially for reading only operation. At this moment, I attributed my problem to my frequent writing to the USB drive. I constantly bring work home with the USB drive and, therefore, writing to the USB drive quite often. Based on some articles, the writing to USB is in blocks. So, a single change in a file could result in a lot of writings. My proposal is to keep adding to the USB until it is full. I will then deleted the oldest content and reuse that part of the memory. My hope is that by adding to the USB, I am writing across the USB and distribute my writing over the whole USB instead of writing to the same area over and over again. Hopefully this will extend the life of the USB.