"Unknown DNS server error occurred" error prevents HA Pool setup in SolarWinds Platform 2025.2

After upgrading to SolarWinds Platform version 2025.2, users attempting to set up or validate TSIG credentials in the HA Pool DNS Settings may encounter the following error:

Unknown DNS server error occurred.
SolarWinds.HighAvailability.Utilities.Exceptions.DnsManagerException: Error on DNS Operations: Could not load file or assembly 'BouncyCastle.Crypto, Version=1.8.4.0, Culture=neutral, PublicKeyToken=0e99375e54769942' or one of its dependencies. The system cannot find the file specified.
---> System.IO.FileNotFoundException: Could not load file or assembly 'BouncyCastle.Crypto, Version=1.8.4.0, Culture=neutral, PublicKeyToken=0e99375e54769942' or one of its dependencies. The system cannot find the file specified.
   at SolarWinds.HighAvailability.Utilities.Dns.DnsManagerBase.RetryWithResponse(...)
   at SolarWinds.HighAvailability.Utilities.Dns.BindDnsManager.SendCheckUpdate(...)
   at SolarWinds.HighAvailability.Utilities.Dns.BindDnsManager.CheckDnsZone()
--- End of inner exception stack trace ---
   at SolarWinds.HighAvailability.Utilities.Dns.BindDnsManager.CheckDnsZone()
   at SolarWinds.Orion.HighAvailability.Common.Plugins.HAPlugin.CheckDnsZone(...)

In the HighAvailability.Service.log at C:\ProgramData\SolarWinds\Logs\HighAvailability, you may also see:

INFO  SolarWinds.HighAvailability.Utilities.Dns.DnsManagerBase - DNS query attempt failed: Could not load file or assembly 'BouncyCastle.Crypto, Version=1.8.4.0, Culture=neutral, PublicKeyToken=0e99375e54769942' or one of its dependencies.
System.IO.FileNotFoundException: Could not load file or assembly 'BouncyCastle.Crypto, Version=1.8.4.0, Culture=neutral, PublicKeyToken=0e99375e54769942' or one of its dependencies.

This issue prevents completion of HA pool setup and DNS updates from being validated during TSIG credential testing.

The issue is caused by a missing DLL file BouncyCastle.Crypto.dll, which is required for DNS TSIG cryptographic operations. This DLL may not be deployed or registered correctly during the SolarWinds Platform 2025.2 installation or upgrade process.

Note: Take a backup of your SolarWinds Platform database and disable High Availability globally before proceeding with the steps below.

To resolve this problem, please upgrade to SolarWinds Platform 2025.2.1 and above.  If upgrade is not possible, perform the steps below:

1. Navigate to the SolarWinds Platform installation folder.
   Default path:
   

   C:\Program Files\SolarWinds\Orion\Web\api2\bin

   (Location may vary depending on installation path.)
2. Locate the file BouncyCastle.Crypto.dll.
3. Copy this file and paste it into:
   

   C:\Program Files\SolarWinds\Orion\

   (Ensure you paste it at the root of the Orion installation directory.)
4. Open Database Manager.
5. Locate and open the Settings table.
6. Search for the setting:
   

   Settings_BindDnsTsigAlgorithm

7. If you are using MD5 encryption, ensure the value is set to 1. Use the following query to verify and update:
   

   -- Scripts are not supported under any SolarWinds support program or service.
   -- Scripts are provided AS IS without warranty of any kind. SolarWinds further
   -- disclaims all warranties including, without limitation, any implied warranties
   -- of merchantability or of fitness for a particular purpose. The risk arising
   -- out of the use or performance of the scripts and documentation stays with you.
   -- In no event shall SolarWinds or anyone else involved in the creation,
   -- production, or delivery of the scripts be liable for any damages whatsoever
   -- (including, without limitation, damages for loss of business profits, business
   -- interruption, loss of business information, or other pecuniary loss) arising
   -- out of the use of or inability to use the scripts or documentation.
   
   SELECT * FROM [dbo].[Settings] WHERE name = 'Settings_BindDnsTsigAlgorithm'

   
   

   -- Scripts are not supported under any SolarWinds support program or service.
   -- Scripts are provided AS IS without warranty of any kind. SolarWinds further
   -- disclaims all warranties including, without limitation, any implied warranties
   -- of merchantability or of fitness for a particular purpose. The risk arising
   -- out of the use or performance of the scripts and documentation stays with you.
   -- In no event shall SolarWinds or anyone else involved in the creation,
   -- production, or delivery of the scripts be liable for any damages whatsoever
   -- (including, without limitation, damages for loss of business profits, business
   -- interruption, loss of business information, or other pecuniary loss) arising
   -- out of the use of or inability to use the scripts or documentation.
   
   UPDATE [dbo].[Settings]
   SET CurrentValue = '1'
   WHERE name = 'Settings_BindDnsTsigAlgorithm'

   Mapping Reference:
   

   0 = Unknown, 1 = Md5, 2 = Sha1, 3 = Sha256, 4 = Sha384, 5 = Sha512

8. Save the change (if using the Enable Table Editing option).
9. Restart all SolarWinds Platform services on the active server.
10. Retry the TSIG validation and check the HighAvailability.Service.log to confirm if the issue is resolved.