I have seen issues when the Data on the Device is the issue. Try the following.
1. Backup your device user Backup/Restore on the Blackberry Desktop Manager.
2. Go to advanced and "Clear" your Address book / Calendar / Tasks / Memos.
*NOTE* If you can not do this then you are running off of a BES 4.0 system and should be consulting your BES Admin
3. Sync again.
If you still get the issues you can Restore the Data items using the Backup / Restore applications again.