Bad ecc error in 16bit nand flash

Hi all,
I m using the 16bit Nand flash from the STMicro on a arm based CPU.I m selecting the option of calculating and storing the ecc on the out of bound data.When I write some data on the nand and read the same data I m getting the Bad ECC error.Can someone plase tell me that is there any problem in the data writing to the Nand

Bye