I have this problem last week and after much research done, there is still no solution for this.
Just want to share some of the solution which I have tried but there is still no success. Hopeless!
Solution Attempt #1
1. Click Start, click Run, type regedit.exe in the Open box, and then click OK.
2. In Registry Editor, locate and then click the following registry subkey:
3. On the Edit menu, point to New, and then click Multi-String Value.
4. Rename the multi-string value as "ReservedPorts," and then double-click ReservedPorts.
5. In the Value data box, type 1723-1723, and then click OK.
6. Quit Registry Editor.
Solution Attempt #2
Use the netstat command to find the program that uses port 1723. Then, end the process for that program. To do this, follow these steps:
1. Click Start, click Run, type cmd.exe in the Open box, and then click OK.
2. At the command prompt, type the following command, and then press ENTER: netstat -aon
3. In the output that is displayed, identify the process ID for the program, if any, that uses TCP port 1723.
4. At the command prompt, type the following command, and then press ENTER: taskkill /PID PID /F
*Note The taskkill command ends the process that corresponds to the process ID number. The /F option is used to forcefully end the process.
5. At the command prompt, type exit, and then press ENTER to quit the command prompt.
6. Restart your computer. This may cause the program that uses TCP port 1723 to use a different port.
Findings: Noted that the taskkill command failed to kill any process at all, wonder whether it is still applicable now? So last resolution will be to re-format & reinstall the Window Vista!