How to fix Error 261 on Windows Server 2025 / Windows 11

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Troubleshooting Guide: SQL Server Error 261 – “‘%.*ls’ is not a recognized function”

Why This Error Happens

This error occurs when SQL Server 2025 parses a T-SQL statement referencing a function name that does not exist in the current database scope, is misspelled, or lacks the required schema prefix. It is commonly triggered after a database migration or restore where user-defined functions (UDFs) failed to script over correctly, or when an application connects to the wrong database/schema context that lacks the expected function definitions. Additionally, this can occur if a function was recently deprecated or removed in SQL Server 2025 and legacy application code still references it.

Step-by-Step Resolution Guide

Step 1: Verify the Function Exists in the Target Database

  • Connect via SQL Server Management Studio (SSMS) or Azure Data Studio to the instance reporting the error.
  • Run SELECT * FROM sys.objects WHERE type IN ('FN', 'IF', 'TF') AND name = 'YourFunctionName'; to confirm the function is present.
  • Check if the function exists under a different schema (e.g., dbo vs a custom schema) using SELECT SCHEMA_NAME(schema_id), name FROM sys.objects WHERE name = 'YourFunctionName';.

Step 2: Correct the Schema Reference in the Query

  • Update the failing query or stored procedure to explicitly prefix the function call with its schema, e.g., change MyFunction() to dbo.MyFunction().
  • Check application connection strings in web.config, app.config, or ODBC/DSN settings on Windows Server 2025 / Windows 11 to ensure the Initial Catalog (database) matches the one containing the function.
  • Save and redeploy the corrected script or stored procedure.

Step 3: Recreate Missing or Corrupted Function Objects

  • If the function is confirmed missing, restore it from a source-controlled script or a recent backup.
  • Open the original .sql deployment file and re-execute the CREATE FUNCTION statement in the correct database context using USE [YourDatabase]; GO before the creation script.
  • Validate object dependencies using sp_depends 'dbo.YourFunctionName'; to ensure no linked objects are also missing.

Step 4: Check for Deprecated or Renamed Built-in Functions

  • Review the SQL Server 2025 “Breaking Changes” documentation, as some legacy built-in functions may have been renamed or removed in this release.
  • Search application code and stored procedures for the deprecated function name using SSMS’s “Find in Files” or sys.sql_modules query: SELECT * FROM sys.sql_modules WHERE definition LIKE '%OldFunctionName%';.
  • Replace deprecated calls with the SQL Server 2025 supported equivalent function.

Alternative or Verification Steps

  • Re-run the original failing query or application transaction and confirm Error 261 no longer appears in the SQL Server Error Log (Event Viewer > Applications and Services Logs > MSSQLSERVER on Windows Server 2025/Windows 11).
  • If the issue persists, use sp_helptext 'YourFunctionName' to inspect the function’s actual T-SQL definition for syntax errors introduced during a prior migration, and re-deploy from a clean backup if corruption is confirmed.