How to Fix QUOTA UNDERFLOW (0X00000021) BSOD on Windows 10 & 11

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How to Fix QUOTA UNDERFLOW (0X000021) BSOD on Windows 10 & 11

The QUOTA UNDERFLOW (0X00000021) Blue Screen of Death (BSOD) is a frustrating error that can suddenly appear on your Windows 10 or 11 PC, causing it to crash and restart. This error typically occurs when the system encounters an issue with disk quotas, often related to file permissions, corrupted system files, or hardware problems. While this BSOD doesnt always indicate severe hardware failure, it can disrupt your workflow. Below, well explain what causes this error and provide step-by-step solutions to resolve it.

What Causes the QUOTA UNDERFLOW (0X000021) Error?

The QUOTA UNDERFLOW BSOD usually appears when Windows tries to access a file or resource but encounters an unexpected condition, such as:

  • Corrupted system files: Damaged or missing critical system components can trigger this error.
  • Disk quota issues: Problems with disk space allocation or permissions may cause the system to misbehave.
  • Outdated or incompatible drivers

    • : A faulty driver, especially for storage devices (like SSDs or HDDs), can lead to this error.

  • Malware or virus infections

    • : Some malware may interfere with system processes, causing instability.

  • Hardware conflicts

    • : Faulty RAM, a failing hard drive, or overheating can also contribute to the issue.

How to Fix QUOTA UNDERFLOW (0X000021) BSOD

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Method 1: Run System File Checker (SFC) and DISM

The first step is to repair corrupted system files using built-in Windows tools. These commands scan for errors and restore missing or damaged files.

  • Open Command Prompt as Administrator:
    • Press Win + X, then select Terminal (Admin) or Command Prompt (Admin).
  • Run System File Checker (SFC):
    • sfc /scannow

    Wait for the scan to complete. If errors are found, they will be repaired automatically.

  • Run DISM (Deployment Image Servicing and Management):
    • DISM /Online /Cleanup-Image /RestoreHealth

    This may take several minutes. Restart your PC afterward.

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Method 2: Check Disk for Errors with CHKDSK

If the issue is related to disk corruption, use CHKDSK to scan and repair bad sectors.

  • Open Command Prompt as Administrator:
    • Press Win + X, then select Terminal (Admin) or Command Prompt (Admin).
  • Run CHKDSK with the following command:
    • chkdsk C: /f /r

    Replace C: with your system drive if needed. If prompted, schedule the scan for the next reboot.

  • Restart your PC and let the scan complete.

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Method 3: Update or Reinstall Problematic Drivers

Outdated or conflicting drivers can cause BSOD errors. Heres how to update them:

  • Open Device Manager:
    • Press Win + X, then select Device Manager.
  • Look for devices with a yellow exclamation mark (problematic drivers).
  • Right-click the device and select “Update driver.”
  • If updating doesnt work, uninstall the driver:
    • Right-click the device, then select Uninstall device.
    • Check “Delete the driver software for this device” (if available), then restart your PC.
  • Reinstall the driver:
    • Visit the manufacturers website to download the latest driver or use Windows Update.

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Method 4: Check for Malware and Run a Full Scan

Malware can corrupt system files, leading to BSOD errors. Use Windows Defender or a trusted antivirus:

  • Open Windows Security:
    • Press Win + I, go to Update & Security > Windows Security > Virus & threat protection.
  • Run a full scan:
    • Click Quick scan or Scan options > Full scan.
  • Follow the prompts to quarantine or remove threats if detected.

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Method 5: Test for Hardware Issues

If the error persists, hardware problems (like RAM or disk failure) may be the cause. Run these checks:

  • Test your RAM:
    • Press Win + R, type mdsched.exe, and press Enter.
    • Select Recommended (standard) and follow the prompts to test memory.
  • Check your hard drive health:
    • Open File Explorer and right-click your system drive (usually C:).
    • Select Properties > Tools > Check. Choose Scan drive.
  • Monitor temperatures:
    • Use third-party tools like HWMonitor to check CPU/GPU temperatures. Overheating can cause BSODs.

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Method 6: Perform a Clean Boot (If Needed)

A clean boot helps identify if third-party software is causing the issue:

  • Open Task Manager:
    • Press Ctrl + Shift + Esc, go to the Startup tab, and disable all items.
  • Restart your PC in Safe Mode:
    • Hold Shift while clicking Restart from the Start menu.
  • If the BSOD doesnt appear, re-enable items one by one to identify the culprit.

FAQ About QUOTA UNDERFLOW (0X000021) BSOD

Q: Will this error delete my files?

A: No, the BSOD itself doesnt harm your data. However, if its caused by a failing hard drive, back up important files immediately to prevent data loss.

Q: How often does this error occur?

A: It can happen randomly, but frequent occurrences suggest an underlying issue (e.g., driver problems or hardware failure).

Q: Can I ignore it if my PC works fine after a restart?

A: No. The error may return, so apply the fixes above to prevent future crashes.

Q: Is this related to disk quotas in Windows?

A: Yes, but not directly. It often appears when Windows fails to manage disk resources properly due to corruption or driver issues.

Q: Should I reinstall Windows if nothing works?

A: Only as a last resort. Try the methods above firstmost cases are resolved without a full reinstall.

Final Thoughts

The QUOTA UNDERFLOW (0X000021) BSOD is usually fixable with system repairs, driver updates, or hardware checks. Start with sfc /scannow, DISM, and chkdsk. If the issue persists, test your hardware and consider professional diagnostics if needed. By following these steps, you can stabilize your system and prevent future crashes.

If youve tried all methods and still see the error, share details in the commentswere here to help!

Last Updated: December 13, 2025

Tested on: Windows 10 (22H2) & Windows 11 (23H2)

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