How to fix Error 4830 on Windows Server 2025 / Windows 11

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Why This Error Happens

This error occurs because SQL Server’s bcp utility or BULK INSERT command detected a Byte Order Mark (BOM) at the beginning of the data file, indicating it is Unicode-encoded, while the command explicitly specified -c (char) as the data file type. SQL Server automatically overrides the user-specified type to widechar to prevent data corruption, but this triggers Error 4830 as a warning/notice that the explicit configuration did not match the actual file encoding. This is typically caused by a mismatch between the export format of the source file and the import parameters used in the format file or command-line switches.

Step-by-Step Resolution Guide

Step 1: Verify the Actual File Encoding

  • Open the source file (e.g., data.csv or data.txt) in a hex editor or Notepad++.
  • Check for a BOM signature at the start of the file: FF FE (UTF-16 LE) indicates Unicode/widechar.
  • If no BOM is present but the error still occurs, check for embedded null bytes between characters, which also signals Unicode encoding.

Step 2: Update the BCP Command Syntax

  • Navigate to the command prompt or PowerShell session on Windows Server 2025/Windows 11.
  • Locate the bcp command being executed, typically found in a .bat script or SSIS job step.
  • Replace the -c (char) flag with -w (widechar) to match the file’s actual encoding:
  bcp YourDatabase.dbo.YourTable in "C:\Data\source_file.txt" -w -T -S localhost
  • If using BULK INSERT via T-SQL, update the DATAFILETYPE argument from 'char' to 'widechar' in the WITH clause.

Step 3: Correct the Format File (If Applicable)

  • Open the associated .fmt file located in your import directory (e.g., C:\ImportFiles\table.fmt).
  • Check the top-level field type declarations; ensure they read SQLNCHAR or SQLNVARCHAR instead of SQLCHAR for Unicode fields.
  • Regenerate the format file if necessary using:
  bcp YourDatabase.dbo.YourTable format nul -w -T -f "C:\ImportFiles\table.fmt" -S localhost

Step 4: Re-Export the Source File (If Encoding Must Stay ANSI)

  • If char type is actually required for downstream compatibility, re-export the source file without Unicode encoding.
  • In the originating application (e.g., Excel, SSMS Export Wizard), select “CSV UTF-8 (without BOM)” or “ANSI” encoding instead of “Unicode Text.”
  • Re-run the original bcp or BULK INSERT command with -c once the file encoding is confirmed as single-byte ANSI.

Alternative or Verification Steps

  • Run the import again and confirm Error 4830 no longer appears in the SQL Server Error Log (Management > SQL Server Logs in SSMS) or command output.
  • Query the destination table row count against the source file line count to ensure no truncation or encoding corruption occurred during the bulk load:
  SELECT COUNT(*) FROM YourDatabase.dbo.YourTable;