Error Killing jtdxjt9.exe Process KillByName return code

This looks like, JTDX is started and terminated - without ending jtdxjt9.exe - and started again.
In this case, the jtdxjt9.exe task is still active.

a.) Try to start the jtdx.exe as Admin. Go to the program folder and right mouse click on jtdx.exe
and select 'start as admin' (or whatever it says in your language settings).

b.) other solution would be to write a short batch file with

taskkill /f /im jtdx.exe
taskkill /f /im jtdxjt9.exe
start "" jtdx.exe

Nevertheless, you have to find out, what's wrong with your Windows setup.

c.) next solution could be to start JTDX in Windows 8 mode (has no disadvantages)
right click on JTDX.exe and 'Properties' and 'Compatibility mode'
select Windows 8 in the field

Best is launch jtdx from command prompt, usually there will be some hint about the problem.

In general problem is why it was leaved open, just killing will help until next time.