I was running into the same problem. My old system was XP 32-bit, and new system is Windows7 64-bit. Both using SQL Express 05. I managed to fix it by going into Configuration Manager and creating a new x86 platform with the copy settings set to <Empty>. If you already have an x86 option, try deleting and re-creating.

We are also working on 64-bit software the throws a ""SynchronizationAgent" can only be used if the object presents an existing object in the server". I think it is also a 64/32-bit issue. None of the current solutions out there I've found seem to work for me.