How to fix Error 8555 on Windows Server 2025 / Windows 11

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Troubleshooting Guide: SQL Server Error 8555 — RegCloseKey Failed

Why This Error Happens

Error 8555 occurs when the SQL Server service account lacks sufficient permissions to properly close a registry key handle during a read/write operation, typically within the HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SQL Server hive. This is commonly triggered by corrupted registry permissions, overly restrictive Group Policy settings applied to Windows Server 2025, or a registry handle leak caused by an interrupted SQL Server update or patch installation. In rare cases, third-party security or antivirus software intercepting registry calls can also cause the handle closure to fail.

Step-by-Step Resolution Guide

Step 1: Verify Service Account Permissions on the Registry Hive

  • Open regedit.exe as Administrator and navigate to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SQL Server.
  • Right-click the key, select Permissions, and confirm the SQL Server service account (e.g., NT Service\MSSQLSERVER) has Full Control.
  • If missing, click Add, enter the service account name, and grant Full Control, then click Advanced > Replace all child object permissions.

Step 2: Check and Repair Registry Key Corruption

  • Run sfc /scannow from an elevated Command Prompt to repair corrupted Windows system files that may affect the registry structure.
  • Use regedit to export the Microsoft SQL Server key as a backup before making changes:
  • reg export "HKLM\SOFTWARE\Microsoft\Microsoft SQL Server" C:\Backup\SQLRegBackup.reg
  • If corruption is confirmed via Event Viewer (Application log, source: MSSQLSERVER), consider restoring from a known-good registry backup.

Step 3: Review Group Policy and Security Software Interference

  • Open gpedit.msc and check Computer Configuration > Windows Settings > Security Settings > Local Policies > Security Options for any restrictive registry access policies.
  • Temporarily disable third-party antivirus or endpoint protection software to rule out registry call interception.
  • Re-run the SQL Server operation that triggered the error to see if it completes without Error 8555.

Step 4: Reinstall or Repair the SQL Server Instance

  • Launch SQL Server Installation Center from the Start Menu.
  • Select Maintenance > Repair, choose the affected instance, and follow the wizard to restore corrupted registry entries tied to the SQL Server installation.
  • Restart the SQL Server (MSSQLSERVER) service via services.msc after the repair completes.

Alternative or Verification Steps

  • Check the Windows Event Viewer (Application log) for recurrence of Event ID 8555 after completing the steps above; absence of new entries confirms resolution.
  • If the issue persists, run SQL Server as a different service account (e.g., switch from Local System to a dedicated domain service account) via SQL Server Configuration Manager, then restart the service to test.