If you disable a COM port in Device Manager and then run the automatic detection feature for the first time by using the Add Hardware Wizard, the disabled COM port is detected as new hardware. This problem occurs if your computer uses Advanced Configuration and Power Interface (ACPI).

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Because of the various types of COM port implementations on existing computers, Windows has to enumerate COM ports in various ways for compatibility reasons. Windows must check the COM port devices for duplicates to avoid conflicts with other devices.

If you disable an ACPI COM port in Device Manager, Windows cannot detect the resource conflict; the COM port is regarded as new hardware when the you run the Add Hardware Wizard.

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This problem typically does not occur until you reboot the computer. To avoid this problem, do not click Install Communication Port when the COM port is detected by the Add Hardware Wizard. If you install the port, an additional incorrect COM port is added in Device Manager.

To clear the incorrect COM ports in Device Manager, delete in Device Manager all the COM ports that are not active. When you next start your computer, the COM ports are detected correctly.

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Microsoft has confirmed that this is a problem in the Microsoft products that are listed at the beginning of this article.

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