Hi,
I am making a very serious effort to use Micro Visual with
Micro Visual Studio 2015, big system,  but I think I am beginning to  succeed.
I have been debugging then modifying a sketch Rebuilding and attempting to download to Arduino Uno. This fails with the following msg

Upload failed
         System wide configuration file is "C:\Users\Frank\Desktop\arduino-1.6.5-r5\hardware\tools\avr/etc/avrdude.conf"
         Using Port                    : COM13
         Using Programmer              : arduino
         Overriding Baud Rate          : 115200
avrdude: ser_open(): can't open device "\\.\COM13": The system cannot find the file specified.
avrdude done.  Thank you.
Checked Device Manager and COM13 is connected.
I suspect some other part of the system has not released COM13. What could be retaining it and how do I solve it.
So far I have been creating a new project as a temporary solution but of course it is not the solution.
Please help
Thank you