How to fix Error 3262 on Windows Server 2025 / Windows 11

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Why This Error Happens

Error 3262 is generated by the SQL Server backup/restore engine when it performs a checksum validation pass (via BACKUP ... WITH CHECKSUM or RESTORE VERIFYONLY) and detects that the backup media header reports a valid set, yet the underlying page checksums were skipped, mismatched, or partially unreadable due to media-level corruption. This typically occurs because the backup file was written to an unstable storage target—such as a network share with intermittent connectivity, a USB/external drive with write-caching issues, or a volume with disk-level errors—causing bit-level corruption that the SQL Server engine flags inconsistently. It can also surface when antivirus or backup-agent software locks or modifies the .bak file mid-write, resulting in a backup set that passes header validation but fails deeper integrity checks.

Step-by-Step Resolution Guide

Step 1: Verify the Integrity of the Backup File

  • Run RESTORE VERIFYONLY FROM DISK = 'D:\Backups\YourDB.bak' WITH CHECKSUM; in SSMS to confirm whether checksum errors are reported alongside the 3262 message.
  • Check the SQL Server Error Log (ERRORLOG in C:\Program Files\Microsoft SQL Server\MSSQL16.MSSQLSERVER\MSSQL\Log\) for accompanying Error 3183 or 3241, which indicate true corruption versus a benign informational notice.

Step 2: Rule Out Storage and Network Instability

  • Move the backup destination off any SMB/network share and test writing directly to local storage (e.g., E:\SQLBackups\) to eliminate network packet loss as a cause.
  • Run chkdsk E: /f /r on the backup volume in an elevated Command Prompt to detect and repair underlying disk sector errors.
  • Confirm the storage controller/driver is up to date via Device Manager on Windows Server 2025/Windows 11.

Step 3: Exclude Antivirus and Backup Agent Interference

  • Add an exclusion for the SQL Server backup directory (e.g., D:\Backups\*.bak) and the sqlservr.exe process in Windows Defender or your third-party AV console.
  • Disable any third-party backup agent (e.g., Veeam, Commvault) temporarily and re-run a native BACKUP DATABASE ... WITH CHECKSUM to see if the error disappears.

Step 4: Re-run the Backup with CHECKSUM and Full Logging

  • Execute: BACKUP DATABASE YourDB TO DISK = 'D:\Backups\YourDB_Full.bak' WITH CHECKSUM, STOP_ON_ERROR;
  • If the backup completes without the 3262 message, archive the old corrupted file and replace all downstream backup jobs with the new, verified set.

Step 5: Update SQL Server and Apply Latest Cumulative Update

  • Open SQL Server Setup, check Help > About for current build, and install the latest Cumulative Update for SQL Server 2025 from the Microsoft Update Catalog, as checksum-reporting bugs are occasionally patched in CU releases.

Alternative or Verification Steps

  • After remediation, run RESTORE VERIFYONLY FROM DISK = 'D:\Backups\YourDB_Full.bak' WITH CHECKSUM; and confirm the output only shows the benign “backup set is valid” message with no accompanying error codes (3183/3241).
  • As an alternative, perform a full RESTORE DATABASE ... WITH REPLACE to a test instance to confirm the backup is restorable end-to-end, which is the most reliable verification that no page-level corruption exists.