USB_Init() no longer calls sei() to enable global interrupts - this must now be done in the user application once all init code has run.

Demos/Device/ClassDriver/VirtualSerial/VirtualSerial.c

@@ -76,6 +76,7 @@ int main(void)
 	CDC_Device_CreateStream(&VirtualSerial_CDC_Interface, &USBSerialStream);
 
 	LEDs_SetAllLEDs(LEDMASK_USB_NOTREADY);
+	sei();
 
 	for (;;)
 	{