How to fix Error 500 on Windows Server 2025 / Windows 11

by

Troubleshooting Guide: Error 500 – Table-Valued Parameter Column Mismatch in SQL Server 2025

Why This Error Happens

This error occurs when the application code constructs a DataTable, DbDataReader, or IEnumerable<SqlDataRecord> object that does not structurally match the schema of the user-defined table type (UDTT) defined in SQL Server. Common root causes include a UDTT that was altered (columns added/dropped) without updating the corresponding client-side data contract, a mismatch between a cached application build and the current database schema, or manually constructed SqlMetaData arrays that are out of sync with sys.table_types. Since table-valued parameters (TVPs) require an exact column count and compatible ordinal positions, any drift between client and server definitions triggers this validation failure immediately upon execution.

Step-by-Step Resolution Guide

Step 1: Verify the Current UDTT Definition in SQL Server

  • Connect to the instance using SQL Server Management Studio (SSMS) or Azure Data Studio.
  • Run the following query to inspect the exact column count and order:
  SELECT c.name, c.column_id, t.name AS data_type
  FROM sys.table_types tt
  JOIN sys.columns c ON tt.type_table_object_id = c.object_id
  JOIN sys.types t ON c.user_type_id = t.user_type_id
  WHERE tt.name = 'YourTableTypeName'
  ORDER BY c.column_id;
  • Confirm this column count matches the number reported in the Error 500 message.

Step 2: Align the Client-Side Data Structure

  • Open the application code (C#, PowerShell, or SSIS package) that populates the DataTable or SqlDataRecord collection.
  • Ensure the number of DataColumn objects added to the DataTable exactly matches the UDTT column count from Step 1.
  • If using SqlMetaData[], verify each array entry matches both the name, ordinal position, and SQL type (e.g., SqlDbType.NVarChar, SqlDbType.Int).
  • Rebuild and redeploy the application binary if running on Windows Server 2025 under IIS or as a Windows Service.

Step 3: Clear Cached Execution Plans and Metadata

  • On the SQL Server instance, force a refresh of cached plans that may reference the outdated type definition:
  DBCC FREEPROCCACHE;
  • Restart the SQL Server service via Services.msc (SQL Server (MSSQLSERVER)) or through SQL Server Configuration Manager to fully clear stale type metadata from memory.
  • If using a connection pool (e.g., ADO.NET, ODBC), restart the application pool in IIS Manager to force new connections to pick up the updated schema.

Step 4: Re-deploy the UDTT if Schema Drift Is Confirmed

  • If the UDTT itself was incorrectly altered, drop and recreate it with the correct column definitions:
  DROP TYPE dbo.YourTableTypeName;
  CREATE TYPE dbo.YourTableTypeName AS TABLE
  (
      Column1 INT,
      Column2 NVARCHAR(100)
      -- match exact structure required by application
  );
  • Grant EXECUTE/REFERENCES permissions again on the new type, as dropping it removes prior grants.

Alternative or Verification Steps

  • Run a manual test execution of the stored procedure from SSMS using a sample TVP populated via DECLARE @TestTable AS YourTableTypeName; to confirm the fix resolves the error outside the application layer.
  • If the error persists, check for multiple UDTTs with the same name across different schemas (e.g., dbo vs. staging) and confirm the application is referencing the fully qualified schema name.