A COOK  I am so VERY VERY frustrated with Missing Sync 6.0.4 I have had the same errors. In my case it is the Contacts / Notes that are not syncing. It appears that they go through BUT then if you make a change Missing Sync duplicates the contact. Even if you ask to find duplicates it does not register them as there is a slight difference. I have been in contact - well I should say I have gone to Missing Sync Tech support and left an email message but have had no response. I have also spent over 1 hr on the phone with a product specialist with Mac and they have had no luck. What has been established is that Missing Sync 5.1.2 works but has its limitations. But the upgrade to 6.0.4 is not compatible with Mac Book Pro even though Mark Space / Missing Sync say that it is. The Product Specialist says that Mark Space / Missing Sync needs to put a fix in for it and do an update. But since you can not get through to them, then I am SOL. Anyone got the fix yet??  
(Version 6.0.4)