Arduino Write Error

Hello 

I installed Firefly 1.0.0.70 64bit and Arduino 1.6.5 (someone says that Firefly doesn't work with newer versions). When I upload Firmata to my Arduino UNO, "UNO Read" works, but when I try "UNO Write", it works for maybe half a second and after it returns this message: 

"Woops, it seems that you tried to start writing data to the Arduino board before opening the Serial Port. Try using the Open Port component to open the serial connection before setting the Start boolean to True."

But my port is opened (gives message starting with "Hoorey!"...). 

I have servo connected and when I move slider, it spins for maybe 0,5 second and after it stops and returns message. When turn off "UNO Write" component and restart "Open Port" component, then it repeats. 

Any ideas how to solve this issue?