This error can be caused by another program that runs in the background and is trying to access the port. In order to solve this, you can try to do a clean boot and try again. To do a clean boot, for Windows Vista or 7, you can try to go to Start and in the search bar type
msconfig.exe and open the resulted service. In the new window that opened, go to General tab and check Selective startup option an be sure to uncheck the Load startup items option. Next, go to the Service tab, check the Hide all Microsoft service option from the bottom of the page, and then click Disable all button. Press OK and restart your computer. For more information regarding this process you can visit the following website.