Error: 21505, Severity: 10, Changes to publication ‘%s’ cannot be merged because it has been marked inactive.
Error: 21506, Severity: 10, sp_mergecompletecleanup cannot be executed before sp_mergepreparecleanup is executed. Use sp_mergepreparecleanup to initiate the first phase of merge meta data cleanup.
Error: 21507, Severity: 10, All prerequisites for cleaning up merge meta data have been completed. Execute sp_mergecompletecleanup to initiate the final phase of merge meta data cleanup.

Error: 21508, Severity: 10, Cleanup of merge meta data cannot be performed while merge processes are running. Cleanup will proceed after the merge processes have completed.
Error: 21509, Severity: 10, Cleanup of merge meta data cannot be performed because some republishers have not quiesced their changes. Cleanup will proceed after all republishers have quiesced their changes.
Error: 21510, Severity: 10, Data changes are not allowed while cleanup of merge meta data is in progress.
Error: 21511, Severity: 10, Neither MSmerge_contents nor MSmerge_tombstone contain meta data for this row.

Error: 21512, Severity: 18, %ls: The %ls parameter is shorter than the minimum required size.
Error: 21514, Severity: 16, Cannot complete the requested operation in the subscription database because a snapshot is currently being delivered to the database. Perform the operation again at a later time. To stop the delivery of the snapshot, stop the Distribution Agent or Merge A
Error: 21515, Severity: 18, Replication custom procedures will not be scripted because the specified publication ‘%s’ is a snapshot publication.
Error: 21516, Severity: 10, Transactional replication custom procedures for publication ‘%s’ from database ‘%s’:
Error: 21517, Severity: 10, Replication custom procedures will not be scripted for article ‘%s’ because the auto-generate custom procedures schema option is not enabled.
Error: 21518, Severity: 10, Replication custom procedures for article ‘%s’:
Error: 21519, Severity: 10, Custom procedures will not be scripted for article update commands based on direct INSERT, UPDATE, or DELETE statements.
Error: 21520, Severity: 10, Custom procedure will not be scripted because ‘%s’ is not a recognized article update command syntax.
Error: 21521, Severity: 16, Some generation values are above the upper limit of %d used in SQL Server 2000. Change the publication_compatibility_level of the publication to 90 to make this work.
Error: 21522, Severity: 16, This article cannot use the ‘%s’ feature because the publication compatibility level is less than 90. Use sp_changemergepublication to set the publication_compatibility_level of publication ‘%s’ to ’90RTM’.
Error: 21523, Severity: 16, Adding column ‘%s’ to table ‘%s’ failed. Articles can have at most %d columns, including columns that have been filtered.
Error: 21525, Severity: 16, A lightweight replica must be anonymous.
Error: 21526, Severity: 16, Article ‘%s’ already belongs to a subscription with a different value for the @lightweight property.

This is applicable on below versions of SQL Server

SQL Server 2005
SQL Server 2008 R2
SQL Server 2012
SQL Server 2014

Hope this was helpful.

Thanks,
SQLServerF1 Team
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