If you’re encountering Windows System Error Code ERROR_166, you’re not alone. This frustrating error can disrupt your workflow and leave your system unstable if not addressed promptly. But don’t worry—we’ve got you covered with a comprehensive, easy-to-follow guide to fix this issue once and for all.
What is Windows System Error Code ERROR_166?
Before we dive into the fix, it’s important to understand what ERROR_166 means. This Windows system error generally refers to:
ERROR_166 (Decimal 166) – The requested operation cannot be performed in full-screen mode.
This error often pops up when a program tries to execute an operation that’s incompatible with full-screen mode, such as changing display settings, switching screen modes, or running an application that depends on windowed display.
Common Causes of ERROR_166
- Running legacy or incompatible applications in full-screen mode.
- Display driver glitches or outdated graphics drivers.
- Corrupted system files affecting display configurations.
- Software conflicts with multiple monitors or remote desktop sessions.
Step-by-Step Guide to Fix Windows System Error Code ERROR_166
Step 1: Restart Your Computer in Normal Mode
Sometimes, a simple restart can clear temporary glitches that cause ERROR_166.
- Save your work and close all applications.
- Click on Start > Power > Restart.
- After reboot, try to execute the task again causing the error.
Pro tip: If this fixed the issue, great! If not, move to the next step.
Step 2: Run the Problematic Application in Windowed Mode
Because ERROR_166 is tied to fullscreen operations, switching to windowed mode often resolves the problem.
- Open the application causing the error.
- Look for display or graphics settings inside the app.
- Change the screen mode from Fullscreen to Windowed or Borderless Window.
- Apply changes and restart the app.
If the issue disappears, this confirms it’s a fullscreen mode conflict.
Step 3: Update Your Graphics Drivers
Outdated or corrupt graphics drivers can trigger ERROR_166. Here’s how to update them:
- Press Windows + X and select Device Manager.
- Expand Display adapters.
- Right-click your graphics card and select Update driver.
- Choose Search automatically for updated driver software.
- Follow the prompts to complete the update.
- Restart your computer.
Alternatively, visit your GPU manufacturer’s website (NVIDIA, AMD, Intel) to download the latest drivers directly.
Step 4: Check for Windows Updates
Sometimes Microsoft releases patches that fix known errors.
- Go to Settings > Update & Security > Windows Update.
- Click Check for updates.
- Install any available updates.
- Restart your PC.
Keeping your system updated is a good practice to avoid such compatibility problems.
Step 5: Run System File Checker (SFC)
Corrupted system files can also cause ERROR_166. The SFC tool scans and repairs them:
- Press Windows + S, type
cmd. - Right-click Command Prompt and choose Run as administrator.
-
Type the command:
sfc /scannow
- Hit Enter and wait until the process completes.
- Restart your system and check if the error persists.
Step 6: Disable Full Screen Optimizations for the Application
Windows’ fullscreen optimization feature can conflict with some apps:
- Right-click the problematic app’s shortcut or executable file.
- Select Properties > Compatibility tab.
- Check Disable fullscreen optimizations.
- Click Apply, then OK.
- Relaunch the app.
Step 7: Adjust Display Settings or Use a Single Monitor Setup
If you’re using multiple monitors or a remote desktop setup, try:
- Disconnecting external displays temporarily.
- Setting your display scaling to 100%.
- Running the app on the primary monitor.
Configuring your display environment more simply can help avoid this error.
Step 8: Reinstall the Problematic Application
If none of the above works, the application installation might be corrupted.
- Open Settings > Apps.
- Find the application causing ERROR_166.
- Click Uninstall.
- Reboot your PC.
- Download and reinstall the latest version of the app.
Wrapping Up
ERROR_166 might seem daunting at first, but with a bit of patience and these detailed steps, you can fix it with ease. Always remember to backup your important files before making significant system changes.
If you found this guide helpful, feel free to share it with friends and colleagues who might be stuck with the same issue. And if you have any questions or run into roadblocks during the process, don’t hesitate to reach out below—we’re here to help!
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Thanks for reading and happy troubleshooting!
