To resolve this issue, perform the following steps on your BlackBerry device.
a. Open the address book from your BlackBerry device
b. Press the menu key
c. Scroll down to options
d. Expand General Options > Actions
e. Set "Allow Duplicates Names" to "No"
You can then use Desktop Manager to delete all the contacts from the phone to synchronize again.
From BlackBerry Desktop Manager > Backup and Restore >
Advanced section > Advanced >
Select Address Book then press the Clear button