NAND Chips - "Erase success and failed writes !!!"

[Srinivasu.Vaduguri at nokia.com]

Hi all,

I am facing a strange problem in some of our devices which uses Samsung 64MB NAND chips.. 
The blocks didnt report any bad blocks initially. But after some days one of the block
Erase is succesfull but reports  "Failed write" after programming the page.. 

And in some devices I found "Erase fails" and write successful.. But in this case "Write-verify" fails..

Anybody faced this problem before.. or has any clues..

Thanx in advance,

regards,
Srini