How to fix Error 4012 on Windows Server 2025 / Windows 11

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Troubleshooting Guide: SQL Server Error 4012 – Invalid TDS Collation

Why This Error Happens

Error 4012 occurs when the Tabular Data Stream (TDS) packet sent to SQL Server 2025 contains a collation identifier that the server cannot recognize or map to a valid collation in its internal collation table. This typically happens due to a mismatch between client driver versions and the server’s collation set, a corrupted sqlncli or msodbcsql driver installation, or an outdated client library attempting to negotiate a collation introduced in a newer SQL Server version that the driver doesn’t understand. It can also surface after an in-place upgrade where system databases retain a legacy collation reference that conflicts with newly introduced server-level collation metadata.

Step-by-Step Resolution Guide

Step 1: Verify and Update Client Drivers

  • Confirm which driver the failing application uses (ODBC, OLE DB, or JDBC) via Event Viewer under Windows Logs > Application.
  • Download and install the latest Microsoft ODBC Driver or msodbcsql18.msi from the official Microsoft Download Center.
  • Restart the application pool or client service after installation to force driver reload.

Step 2: Check Server Collation Configuration

  • Open SQL Server Management Studio (SSMS) and run:
  SELECT SERVERPROPERTY('Collation');
  • Compare this output against the collation expected by the client connection string.
  • If mismatched, update the connection string or application config file (appsettings.json, web.config, or DSN entry) to explicitly specify the correct collation parameter.

Step 3: Rebuild or Repair System Databases

  • Open an elevated Command Prompt on Windows Server 2025.
  • Navigate to the SQL Server binn directory, typically:
  C:\Program Files\Microsoft SQL Server\MSSQL17.MSSQLSERVER\MSSQL\Binn
  • Run a repair install using the setup media:
  setup.exe /QUIET /ACTION=REBUILDDATABASE /INSTANCENAME=MSSQLSERVER /SQLSYSADMINACCOUNTS=BUILTIN\Administrators /SAPWD=<StrongPassword>
  • This resets master, model, msdb, and tempdb collation metadata to a known-good state.

Step 4: Clear TDS Endpoint Cache and Restart Services

  • Open Services.msc on Windows Server 2025 / Windows 11.
  • Restart the SQL Server (MSSQLSERVER) and SQL Server Browser services to flush cached TDS negotiation parameters.
  • If using a named instance, restart the corresponding SQL Server (InstanceName) service as well.

Alternative or Verification Steps

  • Test the fix by connecting via sqlcmd -S <ServerName> -E -Q "SELECT @@VERSION" — a successful connection with no 4012 error confirms resolution.
  • If the error persists, create a new client alias using SQL Server Configuration Manager with explicit TCP/IP protocol settings and a matching collation flag to bypass any cached negotiation data.