We're here to tackle this BackUp Assistant problem, bonyinye.
Depending on which basic phone you have we can check some settings there.
Have you been able to log into the website to either reset the PIN http://bit.ly/SDWYNC or view the PIN in there?
If the site shows the PIN that you are using, then we want to proceed with additional steps to get this awesome feature to work for you again.
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If you can verify your pin to be correct, and its still giving your trouble, you can always RESET your backup assistant. You will then have the option to do a fresh backup, or restore the contacts from your existing backup assistant.
MENU > Media Center > Browse/Download > Backup Assistant > Select Options > Select About > Enter *73738