It seemed to work for me on Win8.1 machine, but not now on Win7 ?
Not sure why this offered code is commented out: while(!DigiMouse.isConnected()) {} //don't run sketch until USB is connected
I decided to make the LED blink to show signs of life and so I could extend the program and get feedback. Like Don't do any active stuff until I click the middle button.
So I made a blink_DM_delay() as a wrapper around DigiMouse.delay();. Code noted below seems to work reliably to give signs of life, why it works now with no change I cannot say - other than I commented out the last five calls to DigiMouse.

() in the sample sketch.
There is a Digistump bootloader driver installed that seems to promote uploading without powering the device when using this. I was seeing error -1 and moved to new USB port then stopped unplugging/resetting and it recognized the driver and worked to upload? Not sure if this is related?
void setup() {
pinMode(1, OUTPUT); //LED on Model A or Pro
DigiMouse.begin(); //start or reenumerate USB - BREAKING CHANGE from old versions that didn't require this
}
bool blinkState = 0;
void blink_DM_delay( int wait ) {
if (blinkState) {
blinkState = 0;
digitalWrite(1, LOW);
}
else {
blinkState = 1;
digitalWrite(1, HIGH);
}
DigiMouse.delay(wait);
}