The problem is most likely caused by an application which is locked in memory which also locked the COM port. My advice is to go to the application's settings and choose another port for the connection. Additionally, re-install the software for the application and the drivers for the GPS (in case there are any). Reboot the computer and then access the Settings again and make sure the COM port is selected properly. It may be COM1, 2, 3, 4, etc. Just switch the ports and attempt a connection until it works. You have 1-5 tries until you get it right, then it should work.
