How to fix Error 4839 on Windows Server 2025 / Windows 11

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Troubleshooting Guide: SQL Server Error 4839 – Invalid Collation Name in Format File

Why This Error Happens

Error 4839 occurs when SQL Server parses a BCP format file (.fmt) and encounters a collation name for a source column that does not match any collation installed on the target SQL Server 2025 instance. This typically happens when a format file is generated on a different server with a different default collation, or when the file is manually edited and a collation name is misspelled, truncated, or uses deprecated syntax. It can also occur if the format file was created against an older SQL Server version whose collation naming conventions are not recognized by SQL Server 2025.

Step-by-Step Resolution Guide

Step 1: Verify the Collation Name in the Format File

  • Open the .fmt file in a text editor (Notepad++ or VS Code recommended for XML format files).
  • Locate the COLLATION attribute for the column referenced in the error (column %d).
  • Compare the string exactly against supported collations using the query:
  SELECT name FROM sys.fn_helpcollations();
  • Check for trailing spaces, incorrect casing, or truncated names (e.g., SQL_Latin1_General_CP1_CI_A vs. a malformed variant).

Step 2: Regenerate the Format File Using the Current Instance

  • Instead of manually editing the file, regenerate it directly against the target SQL Server 2025 instance to guarantee collation compatibility:
  bcp YourDatabase.dbo.YourTable format nul -c -x -f YourTable.xml -S YourServerName -T
  • This ensures all COLLATION attributes match collations actually installed on the destination server.
  • If using a non-XML format file, regenerate with the -n (native) or -c (character) flag matching your original export method.

Step 3: Check Server and Database Collation Alignment

  • Run the following to confirm the server-level default collation:
  SELECT SERVERPROPERTY('Collation');
  • Run this to check database-level collation for the target table’s database:
  SELECT DATABASEPROPERTYEX('YourDatabase', 'Collation');
  • If the format file references a collation not installed (common after OS-level language pack changes on Windows Server 2025), install the required language/collation support via Windows Server language packs or rebuild the instance with the correct collation.

Step 4: Re-run the BCP or BULK INSERT Operation

  • Execute the bulk load again using the corrected or regenerated format file:
  bcp YourDatabase.dbo.YourTable in YourDataFile.dat -f YourTable.xml -S YourServerName -T
  • Monitor the output for successful row count confirmation instead of Error 4839.

Alternative or Verification Steps

  • Verify the fix by running the bulk load against a small sample file (5-10 rows) before processing the full dataset, confirming no collation-related errors appear in the output or SQL Server error log.
  • As an alternative, bypass format file collation issues entirely by using BULK INSERT with the WITH (CODEPAGE = 'ACP', DATAFILETYPE = 'char') options, which lets SQL Server infer column settings without relying on explicit collation declarations in the format file.