Error 633: The modem or other connecting device is already in use

When a user tries to connect to the internet using a modem, Wi-Fi, or an Ethernet connection and comes across Error 633, there are a few things which could possibly be going wrong. Reports of this issue can be allied way back to the days of Windows Vista and have managed to live even today affecting hundreds of Windows 10 users. This guide is a walk-through of this well-documented VPN Error. Read on to understand Error 633 is, its symptoms, causes, and fixes.

The modem (or other connecting device) is either already in use or is not configured properly

error 633

Users affected by this issue see an error message when trying to connect to the internet; it reads – “The modem or other connecting device is either already in use or not appropriately configured.” This error message for VPN Error 633 explicitly indicates the fact that the modem is malfunctioning due to broken configuration. The possible causes of this error are:

  • The WAN Miniport device (found in Device Manager -> Network adapters) associated with your preferred VPN protocol might not be working properly.
  • The TCP port required for the VPN connection might be currently used by another software application.

Sometimes, Error 633 may occur when multiple Internet connections set up on one device or communication port are exploited by another application. Also, the affected modem is not bound to one specific device; hence any model and PC model can be affected.

Troubleshoot Error 633 on Windows 10

The first solution which can fix VPN Error 633 is unplugging or turning off the internet device that you have been using. Once done, try connecting to the internet once again to see if the issue is fixed. If the problem persists, then you try applying the below-given solutions:

  1. Explicitly reserve the TCP port
  2. Use netstat command to find the program that uses port 1723 and end it
  3. Get rid of irrelevant internet device programs
  4. Update network adapter’s drivers
  5. Uninstall (and then reinstall) your Network Adapter

Let’s look at these solutions in detail.

1] Explicitly reserve the TCP port

Open the ‘Run’ dialogue box by hitting ‘Win+R.’

Enter ‘regedit’ and click ‘OK’ to open a registry editor window

In Registry Editor, locate and then click the following registry subkey:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters

On the ‘edit’ menu, follow path New > Multi-String Value

Rename the multi-string value as ‘ReservedPorts’ and then double-click ‘ReservedPorts.’

In the ‘Value data’ box, type ‘1723-1723’, and then click ‘OK’ to save the new value

Exit from Registry Editor and restart your computer

As soon as the system boots up, check to see if this fix worked.

2] Use netstat command to find the program that uses port 1723 and end it

Go to the ‘Start Menu’ and search for ‘cmd.’

On the search result titled ‘cmd’ right-click and choose ‘Run as administrator’ to launch Command Prompt which has administrative privileges

In the command prompt window, type ‘netstat –aon’ and press ‘ENTER.’

In the output which is displayed, identify the process ID (PID) for the program, if any, that uses TCP port 1723 on your system

At the command prompt, type the following and then press ‘ENTER’

taskkill /PID PID /F

Once the taskkill command has been executed, the offending program will be forced closed and TCP port 1723 will have been freed up.

Note: The taskkill command ends the process that corresponds to the process ID number. The /F option is used to forcefully end the process.

Type ‘exit’, and then press ‘ENTER’ to quit the command prompt

Restart your system now. Once the computer boots, the felonious program should start using a TCP port other than 1723, leaving TCP port 1723 free for your internet device.

3] Get rid of irrelevant internet device programs

Your modem could malfunction when your system contains irrelevant programs or applications like internet booster, third-party tools that come with the modem, etc. These programs may not be necessary for your internet modem or system, hence try uninstalling them. Follow these steps:

  1. From the ‘Start Menu’ search for ‘add or remove programs
  2. Click on the search result titled ‘Add or remove programs
  3. Locate the program in question, Right-click on them and then hit ‘Uninstall’ and follow the un-installation process

Once the unwanted app is removed, reboot your system and try to connect the internet.

4] Update network adapter’s drivers

  1. Press ‘Win+R’ to open ‘Run.’
  2. In the ‘Run’ dialog, type ‘devmgmt.msc’ and press ‘Enter’ to launch ‘Device Manager.’
  3. Double-click on the ‘Network Adapters’ section to expand it
  4. Spot the network adapter used by your computer, right-click and select ‘Update Driver Software.’
  5. Select ‘Search automatically for updated driver software’ and wait for Windows to search.

If your system finds updated drivers for your network adapter, it will automatically download and install them. Once done, try to connect to the internet and see if the issue is resolved.

5] Uninstall (and then reinstall) your Network Adapter

Press ‘Win+R’ to open the ‘Run’ dialog

In the ‘Run’ dialog, type ‘devmgmt.msc’ and press ‘Enter’ to launch ‘Device Manager.’

Double-click on the ‘Network Adapters’ section to expand it

Spot the network adapter used by your computer, right-click and select ‘Uninstall.’

Enable the ‘Delete the driver software for this device’ by marking the checkbox

Click ‘OK’ to confirm

Wait for the uninstallation process to complete, once done follow the path click on Action > Scan for hardware changes to direct Windows to reinstall the network adapter and its drivers automatically.

Once the network adapter is reinstalled, reboot your system and check if the issue is gone.

I hope this guide has helped you solve VPN Error 633.

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Ankit Gupta is a writer by profession and has more than 7 years of global writing experience on technology and other areas. He follows technological developments and likes to write about Windows & IT security. He has a deep liking for wild life and has written a book on Top Tiger Parks of India.

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