There are a few things that you might want to check:
- Make sure the port is not used in any other application (such as hyperterminal, another instance of MATLAB etc.). If the port is used by any such application, it will not show up in MATLAB.
- If an object is created in MATLAB but not deleted and cleared correctly - it will not show up in subsequent attempt of using it.
From the output of instrfind, it appears that a serial object for COM14 was created but not cleaned up correctly (it is still available in the memory, which is why instrfind is finding it). Which means as per point 2 above, it will not be available when you try to create another object using the same port.
You might want to check the code to find all the places where you create a serial object and make sure that you are not trying to create multiple objects to the same port. You should use the same object for all your serial communication to that port.