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You’re referencing the wrong binaries.
The path C:\Program Files\Microsoft SQL Server Management Studio 21\Release\Common7 contains SSMS UI / design-time assemblies, not the SDK/runtime assemblies required for compilation. This is why Microsoft.SqlServer.Management and Microsoft.SqlServer.Dts namespaces are missing.
Try the bellow steps, For SQL Server 2025, you must reference SDK assemblies, not SSMS ones.
- Remove all references added from SSMS 21 path (including ManagedDTS, Dts.Design, MaintenancePlanTasks these are design-time only)
- Add references ONLY from this path:
- C:\Program Files\Microsoft SQL Server\170\SDK\Assemblies\
- Required assemblies
- Microsoft.SqlServer.Management.Smo.dll
- Microsoft.SqlServer.Management.Common.dll
- Microsoft.SqlServer.Management.Sdk.Sfc.dll
- Microsoft.SqlServer.DTSRuntimeWrap.dll
- Microsoft.SqlServer.ManagedDTS.dll
- Set Copy Local = False
- Delete bin / obj → Rebuild
- Microsoft.SqlServer.DTSRuntimeWrap.dll
- Microsoft.SqlServer.Management.Sdk.Sfc.dll
- Microsoft.SqlServer.Management.Common.dll
- Microsoft.SqlServer.Management.Smo.dll
Final note:
- SSMS 21 ≠ SQL Server SDK
- SSMS assemblies will always fail at build time
- SDK assemblies under \170\SDK\Assemblies\ are mandatory
If the SDK folder is missing, rerun SQL Server 2025 setup and install Client Tools SDK.
Thanks,
Akhil.