If you did the $200 trade in pre-order promo with Samsung, there are lots of people having problems submitting the rebate online. Here's what worked for me:
It says it will either take the IMEI or the MEID Hex. The 2nd worked. Take off the 0x and the rest of the numbers (at least for me) were the same as the IMEI minus the last #.
Unless I just got lucky on the 3rd submittal try, hope that works for you!