Are you a VPN user who is suddenly seeing “Error 633: The modem is already in use or not configured properly”  in your Windows 10?

A recent update to your Windows 10, another program using VPN port, or outdated modem drivers might be the reason.

Here at Bobcares, we provide 100% white label tech support for VPN providers. Error 633 in Windows 10 is one of the recent errors we helped troubleshoot and fix.

Read on to know more about why this error happens, and how our VPN Engineers fix it for VPN users.


Why this VPN error 633 in Windows 10?

We have found primarily three reasons for this error:

  •           Another program is already using port 1723 that’s often used by VPN programs.
  •           A recently applied Windows “Creator Update”.
  •           Outdated modem drivers.

Let’s see how we fix these issues.


Fixing VPN 633 when port 1723 is occupied by another program

Recently, a VPN user contacted us with a VPN 633 error. Here is how we helped him:

Identifying the program occupying port 1723:

We helped the customer in identifying the program running on port 1723 using:


That gave us the process ID and we asked our customer to kill it using:

taskkill /PID <PID> /F


Reserving the port:

Next, our VPN support Engineers helped him in reserving the port for a VPN connection using the steps.

  1. Open the Registry Editor by running Regedit in the Run dialog box.
  2. Then, select the subkey – HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesTcpipParameters.
  3. In the edit menu, select New>> Multi-String Value.
  4. Name the newly created Multi-String Value as ‘ReservedPorts’ and update the port 1723-1723 in the Value data field.
  5. Click on OK and close the Registry Editor.
  6. Finally,  restart the system.

And, this helped to fix their problem.

Fixing VPN error 633 in Windows 10 due to creator update

In some cases, Windows update changes some of the underlying system settings. In that case, we need to tweak the system settings.


VPN error 633 Windows 10


To fix system settings we help customers to modify the registry as shown:

  1. Run the Regedit and open the Registry Editor.
  2. Then, navigate to the key HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesRasMan.
  3. Select the key RequiredPrivileges and double-click it to open.
  4. Next, append the data SeLoadDriverPrivilege in the Value data field.
  5. Finally,  click OK and restart the system

This fixes the error.


Note: We always recommend the assistance of experts in editing the Registry Editor. Because incorrect modification might even crash the system.

Here, we always take a backup of registry to use in case of changes.


Outdated modem drivers

Similarly, outdated modem drivers also show VPN error 633 in Windows. We help VPN users in updating the modem drivers by providing the steps shown:

  1. Select Device Manager.
  2. Right-click on the Network Adapters.
  3. Select Update Driver Software from the options.
  4. Update all the adapters.
  5. Finally, reboot the system.


Our Experts are always available online for answering any kind of VPN related queries. Just send us the query and get it fixed quickly.


[Need any assistance for fixing VPN errors? Our Experts are available 24/7.]



In short, VPN error 633 in Windows 10 occurs mainly when port for VPN communication is already in use, due to a  Windows creators update, or due to outdated modem drivers. Today, we saw the methods by which our VPN Support Engineers fix this error.



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