Iphone 4S stuck after 6.1 restore - with NAND error message and Itunes Errors 21 and 1611

After upgrading from 5.1.1 to 6.1 all seemed to be OK. It went smooth.

After few hours the AppStore app seemed not be working as it should (no updates showing etc') - so I rebooted teh device.

The device did not boot but was stuck in a loop (Apple logo showing, screen gets dark, and the logo shows gain and so on).

Tried to restore in recovery mode - got error 1611. tried to restore by DFU - got error 21.

I tried restoring from several different computers and I went through all the steps mentioned trying to deal with these errors.

Nothing works.

Then, I noticed that for a part fo a second between each loop restarting - there is a text showing at the top line of the screen, I was able to capture it:

[NAND] s_cxt_boot:88 sftl: error, unclean shutdown; adopted 2874 spans

Does anyone has any idea what it is? seems to be related to a memory issue (NAND being flash memory technology)

Thanks in advance,

Uri