Fix NS_E_DUPLICATE_ADDRESS (0xC00D0037) on Windows

This error means something else is sitting on the same port

You see NS_E_DUPLICATE_ADDRESS (0xC00D0037) and your streaming app, media player, or game just won't connect. I've seen this in Windows Media Center, Plex, and even some older games like Age of Empires II. The fix is simple: find the process that's squatting on the port and shut it down.

Let's do this fast. You'll need an admin command prompt.

Step 1 – Identify which port is in conflict

1. Press Win + R, type cmd, then press Ctrl + Shift + Enter to run as Administrator. You'll see a User Account Control prompt – hit Yes.
2. In the black command window, type this command and press Enter:
   

   netstat -aon | findstr :PORT

   Replace PORT with the actual port number your app uses. For example, if you're dealing with Plex, it's usually 32400. For a media server, maybe 554 or 1755. If you're not sure, skip | findstr :PORT and just run netstat -aon – but be ready to scroll through a long list.
3. Look for a line that says LISTENING. The last column is the PID (Process ID). Write that number down.

What you should see: After running the command, you'll get output like this:

  TCP    0.0.0.0:1755    0.0.0.0:0    LISTENING    4568

The PID 4568 is the culprit.

Step 2 – Kill the process using that PID

1. Open Task Manager by pressing Ctrl + Shift + Esc.
2. If you see the simple view (just running apps), click More details at the bottom.
3. Go to the Details tab. This shows every process with its PID.
4. Find the PID you noted earlier. If you don't see the PID column, right-click any column header (like Name or CPU) and check PID.
5. Right-click that process and choose End task. Confirm if it asks.

That's it. The port is freed. Restart your app – the error should be gone.

Why this works

Every network service needs a unique combination of IP address and port. Windows won't let two programs sit on the same port at the same time. This error happens when your app tries to bind to a port that some other process already claimed. It's not a bug in your app. It's a resource collision. By finding and ending that other process, you give your app exactly what it needs.

Common processes that cause this: another instance of the same program running in the background, a leftover system service (like WMPNetworkSvc), or even malware that opens ports. In my years doing this, I've also seen antivirus software hold ports for its own update service.

Less common variations of the same issue

1. The PID is “System” or PID 4

If netstat shows PID 4 or the process name is System, that port is reserved by the Windows kernel. You can't kill System. The fix here is to change the port your app uses. For example, in Plex, go to Settings > Remote Access and try a different port like 32401. In a media player, look for a network port setting in Options.

2. The IP address is different

Sometimes the error isn't about a port – it's about a duplicate IP address on the network. Windows will show the same error code if another device on your local network has the same IP. To check this:

1. Open Command Prompt as Administrator.
2. Type ipconfig /all and note your IP address.
3. Then type arp -a. Look for the same IP with a different MAC address. If you see it, you have a duplicate IP.

Fix: Set a static IP on your device, or restart your router so DHCP re-assigns addresses.

3. IPv6 vs IPv4

Some apps bind to IPv6 (::) instead of IPv4 (0.0.0.0). If you see [::]:1755 in the netstat output, that's IPv6. You can disable IPv6 on the network adapter temporarily to see if it resolves things. Go to Control Panel > Network and Sharing Center > Change adapter settings. Right-click your adapter, uncheck Internet Protocol Version 6 (TCP/IPv6), then restart your app.

How to prevent this from happening again

Here's what I tell the techs I train:

• Set a static port for your app. Most media servers let you pick the port number. Choose one above 1024 that's not commonly used (like 23456).
• Close apps you don't need. That leftover instance of VLC or Windows Media Player is often the culprit. Check the system tray (notification area) for hidden icons.
• Use a consistent startup order. If two services start at boot and both want the same port, the first one wins. Configure services to start manually in a specific order.
• Check for port conflicts after Windows updates. I've seen Windows 10 update KB4566782 cause WMPNetworkSvc to start unexpectedly and grab port 1755. After an update, run netstat -aon once to be sure.

One last thing – if you're troubleshooting a game or app that always uses a well-known port (like 27015 for Steam games or 7777 for some Minecraft servers), check the game's official forums for a list of common conflicting services. In the years I've done this, the fix has been the same 90% of the time: find the PID, kill it, move on.