Problem while using win32diskimager to create bootable USB

Dear friends,

I'm trying to "Write" Chrome-OS.img to a USB flash which is of size 4GB, Booting Chrome OS from a USB flash. I'm using "win32diskimager-binary" to do that. The problem is when I try to "Write" the image, this error message appears:
(Writing to a physical device can corrupt the device. Are you sure you want to continue?)

When I click "YES", the flash becomes corrupted + doesn't work. Then I use HP USB Format tool to get it back.

So, how to solve this issue please?

I'm following this guide in here:
Click Here

Thanks :-)