USB Device not Recognized Error.

Why this error comes? This problem persist in two ways. All the usb ports will give this error irrespective of what you connect, in this case why it happens is because of a inner conflict in your hardware.
But sometimes all the ports will work properly, except for a single device. If this is the case, then don't worry because obviously the error is with the particular device, so now its time to check for a replacement.

After the prices slashed for pendrives..

Kingston 4 gb, my next new pen-drive is compatible with almost all operating systems such as Windows Vista / XP / 2000, Mac OS and Linux.A solid 5 year warranty makes it a very attractive option.The amount of time taken to transfer the data is within acceptable limits.But, It lacks in encryption, security and backup software.The drive seems slow relatively,it takes around 3 minutes to transfer a 700 MB file.