Synchronization Editor Issues - Initial Synchronization

Hi, i'm currently using 8.1.3, and i'm facing these errors while performing 'Initial Synchronization'.

1)

Synchronization summary
Synchronization objects with errors
Person
Object state New
----------------------------------------------------------------------------
Synchronization s Person
----------------------------------------------------------------------------
Object 50091706 (?)
----------------------------------------------------------------------------
Reason for error [810306] Error during execution of 'SetValues' in logic
module 'VI.DB.Entities.EntityScriptLogic'.
[810126] Employees: Error applying dynamic template for
City on object ().
[810222] Error executing script 'Tmpl_Person_City'.
[810391] Error flushing changes to database.
[810076] Employees: Value in field Central user account
must be unique. Object ***, Michele (***) already
has this value (***).
----------------------------------------------------------------------------

About employee '50091706' the thing I don't understand is why the object that gives error is not correlated with the employee 'Michele' in the "Reasons for error" field neither i want to set the same CentralAccount.

The 'City' template is correct. 

If Len($FK(UID_Locality).City$) > 0 Then
Value = $FK(UID_Locality).City:Text$
else
Value = $FK(UID_PersonHead).City:Text$
End If

2)

----------------------------------------------------------------------------

Object state Loaded
----------------------------------------------------------------------------
Synchronization s Person
----------------------------------------------------------------------------
Object ***, VALENTINA (***)
(<Key><T>Person</T><P>***
------------------f</P></Key>)----------------------------------------------
Reason for error [810391] Error flushing changes to database.
[810076] Employees: Value in field Central user account
must be unique. Object ***, Valentina (***) already
has this value (***).
----------------------------------------------------------------------------

About this error the strange thing is that the fields it tries to update are filled with the same value (no modified values).

And there aren't other employees with the same CentralAccount.

Thanks in advance, 

Giorgio.