However obviously ToolKit cannot access the COM port or no connection to the device.

1.)

Check the Baudrate which is setup in the DTSC-200's Serial Interface #1

-through the HMI push buttons, enter Code first. e.g. 0003 or 0500, then check the baudrate if it is lower than 9600.

(ToolKit only works with baudrate >=9600 kbps) 

-maybe that is the issue?

2.)

ToolKit started as Administrator?

Verify with your IT department if you actually can use the USB port / COM port in anyway