The remote database synchronisation hangs at "Database modifications"

Symptom: I am trying to synchronise my remote database but the synchronisation is hanging at  "Database modifications".
 
Product Details:
Product Family: Act!
Product: Act! Pro, Act! Premium
Version: 2011 and later
 

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Cause:

This error can occur due to damage in the database, or by a known issue that Microsoft has published for Microsfot SQL Server that causes checkpoint operations in Microsoft SQL Server databases to fail due to a duplicate database table row that gets inserted into the back end of the database.

Solution:

Repairing, reindexing and rebuilding the databases

1. Back up the publisher database as well as the remote database(s).
   
   How to back up and restore an Act! database
   Answer ID 19211
    
2. Follow the instructions in the below article for every database synchronising, inluding the main database:
   
   Act! database rebuild and repair procedures
   Answer ID 19642
    
3. Attempt to synchronise your remote database(s)

Removing duplicate database table rows

1. Back up the publisher database as well as the remote database(s).
   
   How to back up and restore an Act! database
   
   
2. Remove the duplicate database table rows with the following article:
   
   Error: "Cannot insert duplicate key row in object 'sys.syscommittab' with unique index 'si_xdes_id'... error 2601" when attempting to back up, copy, repair, create a remote, or synchronize an Act! database
   
   
   
3. Attempt to synchronise your remote database(s)