How to fix Error 4811 on Windows Server 2025 / Windows 11

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Troubleshooting Guide: SQL Server Error 4811 – “Expected the Column Offset in Data Stream for Bulk Copy of Text or Image Data”

Why This Error Happens

This error occurs when the BCP (Bulk Copy Program) data file or bulk insert stream has a malformed or corrupted structure specifically around text, ntext, or image column offsets. It typically arises from a mismatch between the format file (.fmt) definition and the actual data file layout, often caused by manual editing of the format file, incorrect field terminators, or using an incompatible BCP version between the source and destination SQL Server instances. Additionally, this can happen if the data file was generated or transferred (e.g., via FTP) in the wrong mode (ASCII vs. Binary), corrupting the byte offsets SQL Server expects for LOB (Large Object) data pointers.

Step-by-Step Resolution Guide

Step 1: Verify the Format File Integrity

  • Open the .fmt file associated with your bulk copy operation in a text editor (ensure it is not accidentally saved with Word Wrap or different encoding).
  • Check the host file field order against the destination table schema; ensure prefix lengths for text or image columns are explicitly set to 0 if using non-SQL native format.
  • If the file was created on a different server version, regenerate it using: bcp YourDatabase.dbo.YourTable format nul -c -f YourTable.fmt -S ServerName -T

Step 2: Re-export Data Using Native Format

  • Instead of using character mode, switch to Native format to preserve binary offsets for BLOB data types, which resolves most offset calculation errors.
  • Run the export command specifying the -n (native) flag:
    bcp YourDatabase.dbo.YourTable out "C:\Data\export.dat" -n -S ServerName -T
  • Ensure the export path (e.g., C:\Data\) exists on the Windows Server 2025 machine and the SQL Service account has Read/Write permissions to that directory.

Step 3: Check File Transfer Mode (If file moved between servers)

  • If the data file was moved from a Linux/Unix system or via an FTP client to the Windows 11/Server 2025 machine, verify the transfer protocol used.
  • Ensure the transfer was executed in Binary mode, not ASCII mode, as ASCII mode transfer corrupts the byte-offset pointers required for text/image data streams.
  • Re-transfer the file using Binary mode or a direct network share (UNC path) to eliminate transfer corruption.

Step 4: Validate SQL Server Instance Compatibility

  • Confirm that the bcp.exe utility version matches the SQL Server 2025 engine version by running bcp -v in the Command Prompt.
  • If there is a mismatch (e.g., using an SQL Server 2019 client tool against a 2025 instance), update the command-line utilities via the SQL Server 2025 Feature Pack or Microsoft ODBC Driver installer.

Alternative or Verification Steps

  • Verification: Run the import again using the -e error.log flag (e.g., bcp ... -e error.log) to generate an error log; confirm the log is empty and row counts match the source table count.
  • Alternative: If the error persists with BCP, use the SQL Server Import and Export Wizard in SSMS, which handles offset calculations internally and bypasses manual format file errors entirely.