itune wont sync music to Iphone 4.2.1

[vietkool]

I try to sync some music to my iphone but every time I click sync it run back up then after that I look on the iphne screen just blink for second then it stop sync with no message telling what is going on
anyone have the same problem ? how to fix it ?
there is a padlock icon in side the circle on top of status bar nest to the bluetooth icon what is it ?

I got it synced now. Have to go to itune reset sync history

[Cer0]

/Moved. Should get better answers in the correct section.