error 11 firmware 5.1.1 bungled update............

hello everyone,well i brought 3gs off ebay for grandaughter worked for 2 weeks,so i updated to 5.1.1

all i get on itunes now is can not restore error 11.....

i have done a few restores over last few days to no avail

i never noticed any app s for jailbreaking so i believe and brought it as a normal straight phone

by updating it have i done something wrong some were ?

is their anything i can try or do ?

i would be grateful for any help or advice or pointing in the right direction

thanks......

iphone 3gs 8gb ios was 4.2.7