How to fix Error 4840 on Windows Server 2025 / Windows 11

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Troubleshooting Guide: SQL Server Error 4840 — Invalid Bulk Data Source Provider String Property

Why This Error Happens

Error 4840 occurs when SQL Server 2025 parses the connection or provider string used in a BULK INSERT, OPENROWSET(BULK...), or a bulk load operation (such as bcp or a flat file import), and encounters a property name or value that the OLE DB/bulk provider does not recognize. This typically results from a malformed property-value pair (missing quotes, incorrect delimiter, or a typo in a property key like DATA_SOURCE, FORMAT_FILE, or CODEPAGE), an outdated or mismatched provider version, or corrupted format file metadata referenced in the bulk command. It can also surface when a credential or external data source definition used for the bulk operation has an invalid or deprecated property set after a Windows Server 2025 or SQL Server upgrade.

Step-by-Step Resolution Guide

Step 1: Validate the Bulk Command Syntax

  • Open the exact BULK INSERT or OPENROWSET(BULK...) statement that triggered the error and review every property inside the WITH (...) clause.
  • Confirm each property name matches supported syntax exactly (e.g., FIELDTERMINATOR, ROWTERMINATOR, FORMATFILE, DATA_SOURCE) — check for stray commas, missing quotes, or unsupported properties carried over from older SQL Server versions.
  • Example of a common fault: WITH (FORMAT_FILE = 'C:\data\file.fmt') — the correct property is FORMATFILE, not FORMAT_FILE.

Step 2: Inspect the External Data Source and Credential Definition

  • Run SELECT * FROM sys.external_data_sources; to review the LOCATION and TYPE_DESC values tied to the bulk operation.
  • Ensure the LOCATION string (e.g., https://, abs://, or a UNC path like \\FileServer\Share) does not contain invalid characters or unsupported property tags for SQL Server 2025’s updated bulk provider.
  • If using a CREDENTIAL, verify it was created with IDENTITY and SECRET values compatible with the current provider (re-create it if migrated from a legacy SQL Server instance).

Step 3: Verify the Format File and File Path Integrity

  • Open the .fmt or .xml format file referenced in the bulk command and confirm its version header (8.0, 9.0, etc.) matches a version supported by SQL Server 2025.
  • Check that file paths use proper escaping (double backslashes in application code, single backslashes in T-SQL) and that the file exists on a path accessible to the SQL Server service account.
  • Regenerate the format file using bcp <table> format nul -c -x -f newformat.xml -T if corruption or version mismatch is suspected.

Step 4: Update or Repair the Bulk Provider Components

  • On Windows Server 2025 / Windows 11, confirm the “Microsoft OLE DB Driver” and “SQL Server Native Client” (or current MSOLEDBSQL equivalent) are updated via Windows Update or the official Microsoft Download Center.
  • Restart the SQL Server service (services.msc → SQL Server (MSSQLSERVER) → Restart) after any driver update to reload provider libraries.

Alternative or Verification Steps

  • Re-run the original bulk operation in SQL Server Management Studio (SSMS) with SET FMTONLY ON disabled and monitor for Error 4840 recurrence; check SQL Server Error Log (EXEC xp_readerrorlog) for additional context on which property triggered the fault.
  • As an alternative, bypass the suspect property entirely by rebuilding the bulk command using OPENROWSET(BULK...) with minimal default properties, then incrementally re-add optional properties (CODEPAGE, ERRORFILE, etc.) one at a time to isolate the invalid entry.