How to fix Error 9602 on Windows Server 2025 / Windows 11

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Troubleshooting Guide: SQL Server Error 9602 – “Failed to start a system task with error code %d”

Why This Error Happens

This error typically occurs when SQL Server’s internal scheduler is unable to allocate a worker thread for a background system task, often due to resource exhaustion or a misconfigured max worker threads setting. It can also result from insufficient memory reserved for the SQLOS scheduler pool, corrupted system database files (such as tempdb or model), or a Windows-level permission restriction preventing the SQL Server service account from spawning new threads. In some cases, this is triggered by antivirus or endpoint protection software interfering with SQL Server’s process-level thread creation on Windows Server 2025 / Windows 11.

Step-by-Step Resolution Guide

Step 1: Verify SQL Server Service Account Permissions

  • Open Services.msc and locate the SQL Server (MSSQLSERVER) service.
  • Confirm the service account has “Log on as a service” rights under Local Security Policy > User Rights Assignment.
  • Ensure the account is not restricted by Group Policy on Windows Server 2025 domain controllers.
  • Restart the SQL Server service after confirming permissions.

Step 2: Check and Adjust Max Worker Threads Configuration

  • Open SQL Server Management Studio (SSMS) and run:
  EXEC sp_configure 'max worker threads';
  • If the value is non-zero and too low for your workload, reset it to default (0 = auto-configure) using:
  EXEC sp_configure 'show advanced options', 1;
  RECONFIGURE;
  EXEC sp_configure 'max worker threads', 0;
  RECONFIGURE;
  • Restart the SQL Server instance for changes to take effect.

Step 3: Rebuild or Repair TempDB

  • Check the health of tempdb files located at C:\Program Files\Microsoft SQL Server\MSSQL17.MSSQLSERVER\MSSQL\DATA\.
  • Stop the SQL Server service, verify the drive has sufficient free space (minimum 20% recommended), and restart the service.
  • If corruption is suspected, run:
  DBCC CHECKDB (tempdb) WITH NO_INFOMSGS;

Step 4: Exclude SQL Server Processes from Antivirus/EDR Scanning

  • Add exclusions for sqlservr.exe and the data/log directories in Windows Defender or third-party antivirus software.
  • Navigate to Windows Security > Virus & threat protection > Exclusions and add the SQL Server installation path.
  • Restart the SQL Server service and monitor the SQL Server Error Log for recurrence of Error 9602.

Alternative or Verification Steps

  • Check the SQL Server Error Log (ERRORLOG file in the MSSQL\LOG directory) after restarting the service to confirm Error 9602 no longer appears during startup or task execution.
  • If the issue persists, run sp_configure 'max worker threads' again to confirm the value reset correctly, and review Windows Event Viewer > System Log for related resource-exhaustion warnings (e.g., thread pool starvation or memory pressure alerts).