Hi,
yesterday I tried a basic setup; 1 and 2 values. 1 to 9 drops. Had it running for several hours without any issues so not really sure what the problem is at the moment. I am using Win7 64 bit.
What Arduino are you using?
In the Windows app, does the dropController COM appear in the list?
Has the COM port changed?
Can you connect the dropController to the Arduino IDE?
If yes, open the serial monitor (9600) and enter <HELLO> you should get a HELLO back. You can also try <VERSION>