control arduino uno via vb.net and firmata

Hello community,

I'm trying since weeks, to communicate with my arduino-uno with installed firmata-sketch via vb.net.
i've read mutch, but i'm stucking.
i bought a breadboard and established a easy-circuit. arduino-uno, resistor (220 ohm) and a led. after installing a simple sketch on arduino the led ist blinking as i want it to.
now i installed the firmata-sketch on my arduino and startet the test-application. i could easily controll the led via the windows dialog.
i tried to control my led with the example-firmata-project and vb.net 2010. the connect was successful. i activated the digital pin 12 (the one with the circuit on it), switched the mode to output and pushed the button to send the "high"-signal throught the digi-pin 12 - nothing happend. Only the onboard led indicated the serial communication between the vb-app and the arduino. the led does nothing. :~
when i switch to the pwm-mode the test-application crashes after a couple of seconds. then i have to unplug my arduino from power to reset.
does anyone have any sugestion? where could my problem be?
thanks for your help.

Greetings, Frank.

the test-application crashes after a couple of seconds.

Sounds like the problem is with your application.

does anyone have any sugestion? where could my problem be?

In your code. If you posted your VB code, perhaps the specific area/line could be pinpointed, and a solution proposed.