With that option enabled, you cannot even blink an LED. As soon as its disabled, it will begin working again.
Here is a basic sketch to run when your build menu has the USB Support CDC selected that has the issue.
Code: Select all
void setup()
{
pinMode(PA5, OUTPUT);
delay(50);
}
void loop()
{
digitalWrite(PA5, HIGH);
delay(500);
digitalWrite(PA5, LOW);
delay(500);
}