Error 633 VPN - Port already in use

Good Morning

I have a problem with a vehicle computer with Windows 8.1/Windows10 and Modem with SIM card.

On windows startup, I excute an Internet Dial-up connection and after that I execute a Dial-up VPN connection.

Everything works fine as long as the modem will lose the signal; than I get 633 error and I have to restart windows.

The problem does not occur if I use only Dial-up internet connection without VPN connection.

The problem does not occur with Windows 7

I have tried to follow the instructions described in this thread:

I tried to kill RasMan process but after that I lose dial-up connections in "Network connections".

Then, I execute "sc start rasman" and Dial-up connections are available again but I still get 633 Error.

In this state, if I change modem COM port, Internet and VPN connections works fine again so I suppose that some services lock the COM port.

I installed all windows updates but did not solve the problem

I can not ask the customer to restart windows while on the job

Thank you in advance and excuse me for english


Thank you for your quick response.

You can follow steps below to help resolve the Error 633 further:

  1. Press Windows key+R, type regedit in the Run box and then click OK.
  2. In the Registry Editor, locate and then click the following registry subkey:
    • HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services|Tcpip\Parameters
  3. On the Edit menu, point to New and click Multi-String Value.
  4. Rename the multi-string value as ReservedPorts, and then double-click ReservedPorts.
  5. In the Value data box, type the ports used by your VPN so that we may reserve it (i.e. 1723-1723 if the port is only 1723 and not a range of ports).
  6. Exit to Registry Editor.

You can use netstat command to find the program that uses the port. Then end the process for that program.

  1. Type cmd in the search box, right click Command Prompt  and then select Run as Administrator.
  2. In the command prompt type the following command:
    • netstat -aon (A- To display all connections and listening ports, O- To displays the owning process ID associated with each connection, and N- To displays addresses  and  port numbers in numerical form).
  3. At the command prompt, type the following command and press Enter:
    • Taskkill /PID PID /F (The taskkill commands ends the process that corresponds to the process ID number. The /F option is used to forcefully end the process.
  4. Type exit on the command prompt  and press Enter to quit the command prompt.
  5. Restart your computer.

NOTE: It is important to back up first your registry.

Let us know how it goes.


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Question Info

Last updated April 14, 2021 Views 5,008 Applies to: