Error “Device does not exist” when you insert USB COM port device in Windows 7

If you are a regular user of your computer’s USB COM port, chances are high to stumble upon “Device does not exist” error, upon repeated plug and unplug of the USB device. This is a known problem in Windows 7. According to Microsoft, this problem arises due to failure in COM port re-creation, during sudden removal of the USB COM device and connecting it again. The core of the problem is due to accidental removal of the Usbser.sys driver, which is responsible for creating virtual COM ports on your Windows PC.

usb com port error

A official Hotfix is available to download, and fix this problem only, which does have some prerequisites to install.


  1. You should have Windows 7 Service Pack 1 installed before running the hotfix.
  2. You must have security update 2884256 installed.


Once you have applied the above prerequisites, follow the hotfix link, accept the Microsoft’s Terms and Conditions, and then download and run it. After hotfix is installed, restart your computer. Now the USB COM port problem should vanish.

This hotfix applies to

  • Windows 7 Enterprise
  • Windows 7 Professional
  • Windows 7 Starter
  • Windows 7 Ultimate
  • Windows Server 2008 R2 Datacenter
  • Windows Server 2008 R2 Enterprise
  • Windows Server 2008 R2 Foundation
  • Windows Server 2008 R2 Standard.

Kiran Kumar

Hi there! Kiran Kumar is an Engineer by profession, and loves blogging primarily on Microsoft Windows operating system and also enjoys reviewing software and products. Currently, he is exploring Windows 10 and you will see a lot of articles on know-how about it. When he is not writing for TWP, he enjoys time with his Family, listens to lot of music, enjoys Biking, and occasionally plays racing games on Xbox One.