Veeam Backup & Replication upgrade fails with an error "Database version downgrade detected....Reboot and restart the setup"

Challenge

The upgrade to Veeam Backup & Replication U4 fails with "Database version downgrade detected....Reboot and restart the setup". You may find following error in the C:\ProgramData\Veeam\Setup\Temp\BackupSrvLog.log:

***Veeam***  SRV: [31.01.2019 11:39:43]:<00000001> [VEEAM] Database version has been incremented to <5186>
***Veeam***  SRV: [31.01.2019 11:39:43]:<00000001> [VEEAM] Executing version command (ContentType=[Schema], Version=<5186>)
***Veeam***  SRV: [31.01.2019 11:39:43]:<00000001> [VEEAM] Adding trusted hosts (InitialCatalog=[VeeamBackup], DatabaseVersion=<5186>)
***Veeam***  SRV: [31.01.2019 11:39:44]:<00000001> [VEEAM] [SQL|ERROR] declare @id uniqueidentifier;
***Veeam***  SRV: [31.01.2019 11:39:44]:<00000001> [VEEAM] [SQL|ERROR] set @id = '52107791-e0ff-4538-a26e-4717962aef77';
***Veeam***  SRV: [31.01.2019 11:39:44]:<00000001> [VEEAM] [SQL|ERROR] declare @usn bigint;
***Veeam***  SRV: [31.01.2019 11:39:44]:<00000001> [VEEAM] [SQL|ERROR] exec IncrementUsn @usn output;
***Veeam***  SRV: [31.01.2019 11:39:44]:<00000001> [VEEAM] [SQL|ERROR] BEGIN
***Veeam***  SRV: [31.01.2019 11:39:44]:<00000001> [VEEAM] [SQL|ERROR] INSERT INTO [dbo].[Backup.Model.HostSshFingerprint]
***Veeam***  SRV: [31.01.2019 11:39:44]:<00000001> [VEEAM] [SQL|ERROR] (
***Veeam***  SRV: [31.01.2019 11:39:44]:<00000001> [VEEAM] [SQL|ERROR] [id], [network_name], [accepted_fingerprint], [current_fingerprint], [public_key], [agent_id], [network_name_hash], [last_update_time], [usn]
***Veeam***  SRV: [31.01.2019 11:39:44]:<00000001> [VEEAM] [SQL|ERROR] )
***Veeam***  SRV: [31.01.2019 11:39:44]:<00000001> [VEEAM] [SQL|ERROR] VALUES  
***Veeam***  SRV: [31.01.2019 11:39:44]:<00000001> [VEEAM] [SQL|ERROR] (
***Veeam***  SRV: [31.01.2019 11:39:44]:<00000001> [VEEAM] [SQL|ERROR] @id, '<IP Address>', '', '', '', '00000000-0000-0000-0000-000000000000', '', '<Day>/<Month>/Year <time>', @usn
***Veeam***  SRV: [31.01.2019 11:39:44]:<00000001> [VEEAM] [SQL|ERROR] )
***Veeam***  SRV: [31.01.2019 11:39:44]:<00000001> [VEEAM] [SQL|ERROR] END;
***Veeam***  SRV: [31.01.2019 11:39:44]:<00000001> [VEEAM] [SQL|ERROR] GO
***Veeam***  SRV: [31.01.2019 11:39:44]:<00000001> [VEEAM|ERROR] Conversion failed when converting date and/or time from character string. (System.Data.SqlClient.SqlException)

Cause

Solution

1. Open Control Panel.
2. Click on the Clock, Language, and Region link.
3. Click on the Change date, time, or numbers formats link.
4. Under the Formats tab, please set Format: English (United States)
5. Click Apply.
6. Click OK.