2TB wd20earx "The drive cannot find the sector requested"

Yesterday I got this error “The drive cannot find the sector requested” on my 1 month old hdd when trying to copy some data onto it. The drive is about 50% full and I get this error everytime I try to put something on (download with Firefox, Utorrent, …). I immediately downloaded WD data  lifeguard diagnostics tool and ran the test and it passed, but the error still persists. The tool itself only recognises the drive as 1000GB, when it is in fact 2000GB. I only have one partition for the whole drive and Win7 sees it correctly as 1,81TB. All files seem accessible for now. Is there any fix for this or should I send it back for replacement?

If you only did the quick test, also try doing the extended one.

Thank you for your reply. It turned out that the size of the drive was limited with hpa. I used MHDD software to boot up and then restored the full size of the drive. I have no idea why this happened, but luckily now everything works and the data is still there.